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 $46.73   8.380%   $50.646   $50.65   $50.65   $50.60  
  Purchase #2 $184.70   13.324%   $209.3094   $209.31   $209.30   $209.30  
  Purchase #3 $87.83   13.560%   $99.7397   $99.74   $99.75   $99.70  
  Purchase #4 $179.34   8.796%   $195.1147   $195.11   $195.10   $195.10  
  Purchase #5 $140.86   5.360%   $148.4101   $148.41   $148.40   $148.40  
  Purchase #6 $126.93   11.151%   $141.084   $141.08   $141.10   $141.10  
  Purchase #7 $107.92   4.433%   $112.7041   $112.70   $112.70   $112.70  
  7 purchase totals = $874.31       $957.0080   $957.00   $957.00   $956.90