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 $247.85   10.239%   $273.2274   $273.23   $273.25   $273.20  
  Purchase #2 $124.93   10.239%   $137.7216   $137.72   $137.70   $137.70  
  Purchase #3 $138.73   7.573%   $149.236   $149.24   $149.25   $149.20  
  Purchase #4 $206.37   10.139%   $227.2939   $227.29   $227.30   $227.30  
  Purchase #5 $53.28   4.607%   $55.7346   $55.73   $55.75   $55.70  
  Purchase #6 $68.60   6.739%   $73.223   $73.22   $73.20   $73.20  
  Purchase #7 $108.87   7.323%   $116.8426   $116.84   $116.85   $116.80  
  7 purchase totals = $948.63       $1,033.2791   $1,033.27   $1,033.30   $1,033.10