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 $88.88   5.610%   $93.8662   $93.87   $93.85   $93.90  
  Purchase #2 $53.38   11.842%   $59.7013   $59.70   $59.70   $59.70  
  Purchase #3 $224.50   5.154%   $236.0707   $236.07   $236.05   $236.10  
  Purchase #4 $84.48   9.382%   $92.4059   $92.41   $92.40   $92.40  
  Purchase #5 $124.34   11.481%   $138.6155   $138.62   $138.60   $138.60  
  Purchase #6 $186.97   13.791%   $212.755   $212.76   $212.75   $212.80  
  Purchase #7 $44.93   6.335%   $47.7763   $47.78   $47.80   $47.80  
  7 purchase totals = $807.48       $881.1909   $881.21   $881.15   $881.30