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 $62.79   3.491%   $64.982   $64.98   $65.00   $65.00  
  Purchase #2 $6.82   7.819%   $7.3533   $7.35   $7.35   $7.40  
  Purchase #3 $66.53   11.164%   $73.9574   $73.96   $73.95   $74.00  
  Purchase #4 $39.53   4.335%   $41.2436   $41.24   $41.25   $41.20  
  Purchase #5 $78.54   4.604%   $82.156   $82.16   $82.15   $82.20  
  Purchase #6 $87.55   11.464%   $97.5867   $97.59   $97.60   $97.60  
  Purchase #7 $194.63   5.648%   $205.6227   $205.62   $205.60   $205.60  
  7 purchase totals = $536.39       $572.9017   $572.90   $572.90   $573.00