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 $52.41   9.823%   $57.5582   $57.56   $57.55   $57.60  
  Purchase #2 $173.76   12.236%   $195.0213   $195.02   $195.00   $195.00  
  Purchase #3 $42.89   11.216%   $47.7005   $47.70   $47.70   $47.70  
  Purchase #4 $162.51   5.381%   $171.2547   $171.25   $171.25   $171.30  
  Purchase #5 $138.41   11.177%   $153.8801   $153.88   $153.90   $153.90  
  Purchase #6 $165.81   13.232%   $187.75   $187.75   $187.75   $187.80  
  Purchase #7 $149.62   3.563%   $154.951   $154.95   $154.95   $155.00  
  7 purchase totals = $885.41       $968.1158   $968.11   $968.10   $968.30