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 $23.27   8.142%   $25.1646   $25.16   $25.15   $25.20  
  Purchase #2 $246.55   12.340%   $276.9743   $276.97   $276.95   $277.00  
  Purchase #3 $43.25   6.761%   $46.1741   $46.17   $46.15   $46.20  
  Purchase #4 $135.88   5.591%   $143.4771   $143.48   $143.50   $143.50  
  Purchase #5 $127.87   5.333%   $134.6893   $134.69   $134.70   $134.70  
  Purchase #6 $168.29   5.217%   $177.0697   $177.07   $177.05   $177.10  
  Purchase #7 $234.60   5.713%   $248.0027   $248.00   $248.00   $248.00  
  7 purchase totals = $979.71       $1,051.5518   $1,051.54   $1,051.50   $1,051.70