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 $214.95   12.204%   $241.1825   $241.18   $241.20   $241.20  
  Purchase #2 $46.28   7.478%   $49.7408   $49.74   $49.75   $49.70  
  Purchase #3 $232.72   3.867%   $241.7193   $241.72   $241.70   $241.70  
  Purchase #4 $45.84   6.262%   $48.7105   $48.71   $48.70   $48.70  
  Purchase #5 $34.54   4.517%   $36.1002   $36.10   $36.10   $36.10  
  Purchase #6 $93.58   12.415%   $105.198   $105.20   $105.20   $105.20  
  Purchase #7 $102.98   9.463%   $112.725   $112.73   $112.75   $112.70  
  7 purchase totals = $770.89       $835.3763   $835.38   $835.40   $835.30