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 $87.39   5.199%   $91.9334   $91.93   $91.95   $91.90  
  Purchase #2 $127.98   4.834%   $134.1666   $134.17   $134.15   $134.20  
  Purchase #3 $119.78   4.723%   $125.4372   $125.44   $125.45   $125.40  
  Purchase #4 $60.90   9.578%   $66.733   $66.73   $66.75   $66.70  
  Purchase #5 $150.86   13.776%   $171.6425   $171.64   $171.65   $171.60  
  Purchase #6 $213.89   4.729%   $224.0049   $224.00   $224.00   $224.00  
  Purchase #7 $126.64   8.257%   $137.0967   $137.10   $137.10   $137.10  
  7 purchase totals = $887.44       $951.0143   $951.01   $951.05   $950.90