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 $104.46   11.231%   $116.1919   $116.19   $116.20   $116.20  
  Purchase #2 $19.46   8.431%   $21.1007   $21.10   $21.10   $21.10  
  Purchase #3 $244.75   4.437%   $255.6096   $255.61   $255.60   $255.60  
  Purchase #4 $70.75   8.545%   $76.7956   $76.80   $76.80   $76.80  
  Purchase #5 $159.50   9.795%   $175.123   $175.12   $175.10   $175.10  
  Purchase #6 $130.28   6.108%   $138.2375   $138.24   $138.25   $138.20  
  Purchase #7 $73.73   11.156%   $81.9553   $81.96   $81.95   $82.00  
  7 purchase totals = $802.93       $865.0136   $865.02   $865.00   $865.00