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 $98.63   4.716%   $103.2814   $103.28   $103.30   $103.30  
  Purchase #2 $167.96   6.475%   $178.8354   $178.84   $178.85   $178.80  
  Purchase #3 $210.66   11.139%   $234.1254   $234.13   $234.15   $234.10  
  Purchase #4 $148.64   8.391%   $161.1124   $161.11   $161.10   $161.10  
  Purchase #5 $119.31   5.536%   $125.915   $125.92   $125.90   $125.90  
  Purchase #6 $54.73   9.119%   $59.7208   $59.72   $59.70   $59.70  
  Purchase #7 $122.29   9.795%   $134.2683   $134.27   $134.25   $134.30  
  7 purchase totals = $922.22       $997.2587   $997.27   $997.25   $997.20