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 $59.63   8.853%   $64.909   $64.91   $64.90   $64.90  
  Purchase #2 $97.40   11.486%   $108.5874   $108.59   $108.60   $108.60  
  Purchase #3 $107.63   9.623%   $117.9872   $117.99   $118.00   $118.00  
  Purchase #4 $206.42   5.450%   $217.6699   $217.67   $217.65   $217.70  
  Purchase #5 $33.82   12.227%   $37.9552   $37.96   $37.95   $38.00  
  Purchase #6 $178.65   8.468%   $193.7781   $193.78   $193.80   $193.80  
  Purchase #7 $179.88   10.861%   $199.4168   $199.42   $199.40   $199.40  
  7 purchase totals = $863.43       $940.3036   $940.32   $940.30   $940.40