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 $98.25   12.674%   $110.7022   $110.70   $110.70   $110.70  
  Purchase #2 $132.91   10.533%   $146.9094   $146.91   $146.90   $146.90  
  Purchase #3 $213.31   11.398%   $237.6231   $237.62   $237.60   $237.60  
  Purchase #4 $192.83   8.256%   $208.75   $208.75   $208.75   $208.80  
  Purchase #5 $92.28   12.603%   $103.91   $103.91   $103.90   $103.90  
  Purchase #6 $18.68   3.521%   $19.3377   $19.34   $19.35   $19.30  
  Purchase #7 $100.41   5.269%   $105.7006   $105.70   $105.70   $105.70  
  7 purchase totals = $848.67       $932.9330   $932.93   $932.90   $932.90