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 $29.60   11.341%   $32.9569   $32.96   $32.95   $33.00  
  Purchase #2 $239.83   8.723%   $260.7504   $260.75   $260.75   $260.80  
  Purchase #3 $55.62   13.211%   $62.968   $62.97   $62.95   $63.00  
  Purchase #4 $5.40   10.239%   $5.9529   $5.95   $5.95   $6.00  
  Purchase #5 $135.56   6.206%   $143.9729   $143.97   $143.95   $144.00  
  Purchase #6 $174.70   11.379%   $194.5791   $194.58   $194.60   $194.60  
  Purchase #7 $84.82   10.172%   $93.4479   $93.45   $93.45   $93.40  
  7 purchase totals = $725.53       $794.6281   $794.63   $794.60   $794.80