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 $116.72   9.389%   $127.6788   $127.68   $127.70   $127.70  
  Purchase #2 $32.53   4.673%   $34.0501   $34.05   $34.05   $34.10  
  Purchase #3 $113.92   4.575%   $119.1318   $119.13   $119.15   $119.10  
  Purchase #4 $25.43   5.368%   $26.7951   $26.80   $26.80   $26.80  
  Purchase #5 $159.91   8.184%   $172.997   $173.00   $173.00   $173.00  
  Purchase #6 $242.87   5.602%   $256.4756   $256.48   $256.50   $256.50  
  Purchase #7 $23.87   11.685%   $26.6592   $26.66   $26.65   $26.70  
  7 purchase totals = $715.25       $763.7876   $763.80   $763.85   $763.90