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 $60.79   3.241%   $62.7602   $62.76   $62.75   $62.80  
  Purchase #2 $167.66   4.833%   $175.763   $175.76   $175.75   $175.80  
  Purchase #3 $201.88   8.292%   $218.6199   $218.62   $218.60   $218.60  
  Purchase #4 $84.86   3.456%   $87.7928   $87.79   $87.80   $87.80  
  Purchase #5 $95.76   8.202%   $103.6142   $103.61   $103.60   $103.60  
  Purchase #6 $66.56   8.112%   $71.9593   $71.96   $71.95   $72.00  
  Purchase #7 $116.53   10.810%   $129.1269   $129.13   $129.15   $129.10  
  7 purchase totals = $794.04       $849.6363   $849.63   $849.60   $849.70