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 $195.93   11.646%   $218.748   $218.75   $218.75   $218.70  
  Purchase #2 $45.92   13.790%   $52.2524   $52.25   $52.25   $52.30  
  Purchase #3 $46.66   11.779%   $52.1561   $52.16   $52.15   $52.20  
  Purchase #4 $213.25   12.195%   $239.2558   $239.26   $239.25   $239.30  
  Purchase #5 $96.66   8.344%   $104.7253   $104.73   $104.75   $104.70  
  Purchase #6 $14.86   5.486%   $15.6752   $15.68   $15.70   $15.70  
  Purchase #7 $61.58   9.240%   $67.27   $67.27   $67.25   $67.30  
  7 purchase totals = $674.86       $750.0828   $750.10   $750.10   $750.20