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 $73.36   13.686%   $83.4   $83.40   $83.40   $83.40  
  Purchase #2 $31.71   10.357%   $34.9942   $34.99   $35.00   $35.00  
  Purchase #3 $96.69   7.159%   $103.612   $103.61   $103.60   $103.60  
  Purchase #4 $83.83   12.716%   $94.4898   $94.49   $94.50   $94.50  
  Purchase #5 $59.76   8.498%   $64.8384   $64.84   $64.85   $64.80  
  Purchase #6 $159.97   13.809%   $182.0603   $182.06   $182.05   $182.10  
  Purchase #7 $60.37   7.293%   $64.7728   $64.77   $64.75   $64.80  
  7 purchase totals = $565.69       $628.1675   $628.16   $628.15   $628.20