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 $237.30   13.725%   $269.8694   $269.87   $269.85   $269.90  
  Purchase #2 $117.62   5.289%   $123.8409   $123.84   $123.85   $123.80  
  Purchase #3 $128.50   3.146%   $132.5426   $132.54   $132.55   $132.50  
  Purchase #4 $135.39   4.699%   $141.752   $141.75   $141.75   $141.80  
  Purchase #5 $39.94   10.662%   $44.1984   $44.20   $44.20   $44.20  
  Purchase #6 $61.56   8.361%   $66.707   $66.71   $66.70   $66.70  
  Purchase #7 $157.27   11.489%   $175.3388   $175.34   $175.35   $175.30  
  7 purchase totals = $877.58       $954.2491   $954.25   $954.25   $954.20