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 $148.65   7.123%   $159.2383   $159.24   $159.25   $159.20  
  Purchase #2 $111.67   13.432%   $126.6695   $126.67   $126.65   $126.70  
  Purchase #3 $88.86   6.143%   $94.3187   $94.32   $94.30   $94.30  
  Purchase #4 $236.25   5.806%   $249.9667   $249.97   $249.95   $250.00  
  Purchase #5 $64.80   7.238%   $69.4902   $69.49   $69.50   $69.50  
  Purchase #6 $28.57   5.162%   $30.0448   $30.04   $30.05   $30.00  
  Purchase #7 $89.51   5.392%   $94.3364   $94.34   $94.35   $94.30  
  7 purchase totals = $768.31       $824.0646   $824.07   $824.05   $824.00