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 $241.79   7.732%   $260.4852   $260.49   $260.50   $260.50  
  Purchase #2 $171.27   9.502%   $187.5441   $187.54   $187.55   $187.50  
  Purchase #3 $133.91   9.120%   $146.1226   $146.12   $146.10   $146.10  
  Purchase #4 $192.47   13.756%   $218.9462   $218.95   $218.95   $218.90  
  Purchase #5 $139.79   9.770%   $153.4475   $153.45   $153.45   $153.40  
  Purchase #6 $216.43   13.142%   $244.8732   $244.87   $244.85   $244.90  
  Purchase #7 $100.35   8.579%   $108.959   $108.96   $108.95   $109.00  
  7 purchase totals = $1,196.01       $1,320.3778   $1,320.38   $1,320.35   $1,320.30