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 $107.82   5.264%   $113.4956   $113.50   $113.50   $113.50  
  Purchase #2 $55.38   13.555%   $62.8868   $62.89   $62.90   $62.90  
  Purchase #3 $135.78   13.758%   $154.4606   $154.46   $154.45   $154.50  
  Purchase #4 $240.54   8.406%   $260.7598   $260.76   $260.75   $260.80  
  Purchase #5 $63.60   7.425%   $68.3223   $68.32   $68.30   $68.30  
  Purchase #6 $233.84   4.610%   $244.62   $244.62   $244.60   $244.60  
  Purchase #7 $75.43   6.860%   $80.6045   $80.60   $80.60   $80.60  
  7 purchase totals = $912.39       $985.1496   $985.15   $985.10   $985.20