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 $81.98   11.852%   $91.6963   $91.70   $91.70   $91.70  
  Purchase #2 $24.51   11.567%   $27.3451   $27.35   $27.35   $27.30  
  Purchase #3 $239.54   3.338%   $247.5358   $247.54   $247.55   $247.50  
  Purchase #4 $160.58   13.708%   $182.5923   $182.59   $182.60   $182.60  
  Purchase #5 $34.69   10.550%   $38.3498   $38.35   $38.35   $38.30  
  Purchase #6 $246.70   4.643%   $258.1543   $258.15   $258.15   $258.20  
  Purchase #7 $156.26   9.399%   $170.9469   $170.95   $170.95   $170.90  
  7 purchase totals = $944.26       $1,016.6205   $1,016.63   $1,016.65   $1,016.50