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 $207.93   10.592%   $229.9539   $229.95   $229.95   $230.00  
  Purchase #2 $41.70   10.857%   $46.2274   $46.23   $46.25   $46.20  
  Purchase #3 $198.54   10.478%   $219.343   $219.34   $219.35   $219.30  
  Purchase #4 $158.87   6.245%   $168.7914   $168.79   $168.80   $168.80  
  Purchase #5 $46.72   3.416%   $48.316   $48.32   $48.30   $48.30  
  Purchase #6 $32.85   6.478%   $34.978   $34.98   $35.00   $35.00  
  Purchase #7 $121.42   9.497%   $132.9513   $132.95   $132.95   $133.00  
  7 purchase totals = $808.03       $880.5610   $880.56   $880.60   $880.60