Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $235.54   13.359%   $267.0058   $267.01   $267.00   $267.00  
  Purchase #2 $106.25   10.677%   $117.5943   $117.59   $117.60   $117.60  
  Purchase #3 $240.93   12.751%   $271.651   $271.65   $271.65   $271.70  
  Purchase #4 $224.40   12.598%   $252.6699   $252.67   $252.65   $252.70  
  Purchase #5 $148.79   12.222%   $166.9751   $166.98   $167.00   $167.00  
  Purchase #6 $114.87   9.141%   $125.3703   $125.37   $125.35   $125.40  
  Purchase #7 $136.29   7.104%   $145.972   $145.97   $145.95   $146.00  
  7 purchase totals = $1,207.07       $1,347.2384   $1,347.24   $1,347.20   $1,347.40