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 $24.33   10.578%   $26.9036   $26.90   $26.90   $26.90  
  Purchase #2 $231.91   6.490%   $246.961   $246.96   $246.95   $247.00  
  Purchase #3 $213.89   9.858%   $234.9753   $234.98   $235.00   $235.00  
  Purchase #4 $146.57   8.469%   $158.983   $158.98   $159.00   $159.00  
  Purchase #5 $213.30   5.131%   $224.2444   $224.24   $224.25   $224.20  
  Purchase #6 $151.60   13.410%   $171.9296   $171.93   $171.95   $171.90  
  Purchase #7 $237.97   6.123%   $252.5409   $252.54   $252.55   $252.50  
  7 purchase totals = $1,219.57       $1,316.5378   $1,316.53   $1,316.60   $1,316.50