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 $227.40   11.227%   $252.9302   $252.93   $252.95   $252.90  
  Purchase #2 $55.81   6.245%   $59.2953   $59.30   $59.30   $59.30  
  Purchase #3 $189.88   9.158%   $207.2692   $207.27   $207.25   $207.30  
  Purchase #4 $13.64   3.542%   $14.1231   $14.12   $14.10   $14.10  
  Purchase #5 $58.87   13.428%   $66.7751   $66.78   $66.80   $66.80  
  Purchase #6 $124.35   13.200%   $140.7642   $140.76   $140.75   $140.80  
  Purchase #7 $242.53   3.532%   $251.0962   $251.10   $251.10   $251.10  
  7 purchase totals = $912.48       $992.2533   $992.26   $992.25   $992.30