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 $199.71   6.571%   $212.8329   $212.83   $212.85   $212.80  
  Purchase #2 $158.67   9.798%   $174.2165   $174.22   $174.20   $174.20  
  Purchase #3 $65.70   6.626%   $70.0533   $70.05   $70.05   $70.10  
  Purchase #4 $107.43   5.109%   $112.9186   $112.92   $112.90   $112.90  
  Purchase #5 $221.74   11.151%   $246.4662   $246.47   $246.45   $246.50  
  Purchase #6 $125.65   11.295%   $139.8422   $139.84   $139.85   $139.80  
  Purchase #7 $53.54   8.136%   $57.896   $57.90   $57.90   $57.90  
  7 purchase totals = $932.44       $1,014.2257   $1,014.23   $1,014.20   $1,014.20