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 $75.96   8.111%   $82.1211   $82.12   $82.10   $82.10  
  Purchase #2 $15.93   5.246%   $16.7657   $16.77   $16.75   $16.80  
  Purchase #3 $218.31   7.249%   $234.1353   $234.14   $234.15   $234.10  
  Purchase #4 $159.73   3.467%   $165.2678   $165.27   $165.25   $165.30  
  Purchase #5 $97.98   5.323%   $103.1955   $103.20   $103.20   $103.20  
  Purchase #6 $142.85   12.380%   $160.5348   $160.53   $160.55   $160.50  
  Purchase #7 $240.61   8.396%   $260.8116   $260.81   $260.80   $260.80  
  7 purchase totals = $951.37       $1,022.8318   $1,022.84   $1,022.80   $1,022.80