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 $59.65   11.682%   $66.6183   $66.62   $66.60   $66.60  
  Purchase #2 $221.94   7.121%   $237.7443   $237.74   $237.75   $237.70  
  Purchase #3 $65.58   13.421%   $74.3815   $74.38   $74.40   $74.40  
  Purchase #4 $104.28   10.157%   $114.8717   $114.87   $114.85   $114.90  
  Purchase #5 $130.46   7.382%   $140.0906   $140.09   $140.10   $140.10  
  Purchase #6 $221.55   10.519%   $244.8548   $244.85   $244.85   $244.90  
  Purchase #7 $88.70   5.168%   $93.284   $93.28   $93.30   $93.30  
  7 purchase totals = $892.16       $971.8452   $971.83   $971.85   $971.90