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 $32.59   8.381%   $35.3214   $35.32   $35.30   $35.30  
  Purchase #2 $200.70   3.455%   $207.6342   $207.63   $207.65   $207.60  
  Purchase #3 $75.88   13.753%   $86.3158   $86.32   $86.30   $86.30  
  Purchase #4 $31.54   3.552%   $32.6603   $32.66   $32.65   $32.70  
  Purchase #5 $216.39   6.267%   $229.9512   $229.95   $229.95   $230.00  
  Purchase #6 $48.37   12.423%   $54.379   $54.38   $54.40   $54.40  
  Purchase #7 $72.39   5.758%   $76.5582   $76.56   $76.55   $76.60  
  7 purchase totals = $677.86       $722.8201   $722.82   $722.80   $722.90