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 $76.26   6.408%   $81.1467   $81.15   $81.15   $81.10  
  Purchase #2 $54.87   8.828%   $59.7139   $59.71   $59.70   $59.70  
  Purchase #3 $162.71   12.174%   $182.5183   $182.52   $182.50   $182.50  
  Purchase #4 $166.67   12.227%   $187.0487   $187.05   $187.05   $187.00  
  Purchase #5 $185.84   7.744%   $200.2314   $200.23   $200.25   $200.20  
  Purchase #6 $183.32   10.686%   $202.9096   $202.91   $202.90   $202.90  
  Purchase #7 $45.72   8.681%   $49.689   $49.69   $49.70   $49.70  
  7 purchase totals = $875.39       $963.2576   $963.26   $963.25   $963.10