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 $93.41   5.453%   $98.5036   $98.50   $98.50   $98.50  
  Purchase #2 $135.89   10.862%   $150.6504   $150.65   $150.65   $150.70  
  Purchase #3 $52.38   8.756%   $56.9664   $56.97   $56.95   $57.00  
  Purchase #4 $66.79   11.177%   $74.2551   $74.26   $74.25   $74.30  
  Purchase #5 $149.41   10.364%   $164.8949   $164.89   $164.90   $164.90  
  Purchase #6 $248.55   10.643%   $275.0032   $275.00   $275.00   $275.00  
  Purchase #7 $41.88   4.761%   $43.8739   $43.87   $43.85   $43.90  
  7 purchase totals = $788.31       $864.1475   $864.14   $864.10   $864.30