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 $204.94   4.204%   $213.5557   $213.56   $213.55   $213.60  
  Purchase #2 $34.81   4.183%   $36.2661   $36.27   $36.25   $36.30  
  Purchase #3 $119.32   4.827%   $125.0796   $125.08   $125.10   $125.10  
  Purchase #4 $51.68   4.370%   $53.9384   $53.94   $53.95   $53.90  
  Purchase #5 $55.74   8.350%   $60.3943   $60.39   $60.40   $60.40  
  Purchase #6 $241.38   7.367%   $259.1625   $259.16   $259.15   $259.20  
  Purchase #7 $220.83   10.699%   $244.4566   $244.46   $244.45   $244.50  
  7 purchase totals = $928.70       $992.8532   $992.86   $992.85   $993.00