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 $53.34   9.592%   $58.4564   $58.46   $58.45   $58.50  
  Purchase #2 $133.90   10.785%   $148.3411   $148.34   $148.35   $148.30  
  Purchase #3 $204.96   4.217%   $213.6032   $213.60   $213.60   $213.60  
  Purchase #4 $57.61   7.719%   $62.0569   $62.06   $62.05   $62.10  
  Purchase #5 $125.54   9.248%   $137.1499   $137.15   $137.15   $137.10  
  Purchase #6 $168.84   11.667%   $188.5386   $188.54   $188.55   $188.50  
  Purchase #7 $156.62   13.316%   $177.4755   $177.48   $177.50   $177.50  
  7 purchase totals = $900.81       $985.6216   $985.63   $985.65   $985.60