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 $57.64   3.549%   $59.6856   $59.69   $59.70   $59.70  
  Purchase #2 $75.91   10.673%   $84.0119   $84.01   $84.00   $84.00  
  Purchase #3 $111.63   12.691%   $125.797   $125.80   $125.80   $125.80  
  Purchase #4 $223.84   13.419%   $253.8771   $253.88   $253.90   $253.90  
  Purchase #5 $152.78   10.436%   $168.7241   $168.72   $168.70   $168.70  
  Purchase #6 $182.70   3.822%   $189.6828   $189.68   $189.70   $189.70  
  Purchase #7 $46.79   3.747%   $48.5432   $48.54   $48.55   $48.50  
  7 purchase totals = $851.29       $930.3217   $930.32   $930.35   $930.30