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 $90.91   8.514%   $98.6501   $98.65   $98.65   $98.70  
  Purchase #2 $249.57   4.471%   $260.7283   $260.73   $260.75   $260.70  
  Purchase #3 $119.38   7.428%   $128.2475   $128.25   $128.25   $128.20  
  Purchase #4 $201.87   9.407%   $220.8599   $220.86   $220.85   $220.90  
  Purchase #5 $213.80   8.321%   $231.5903   $231.59   $231.60   $231.60  
  Purchase #6 $62.32   11.302%   $69.3634   $69.36   $69.35   $69.40  
  Purchase #7 $224.47   7.492%   $241.2873   $241.29   $241.30   $241.30  
  7 purchase totals = $1,162.32       $1,250.7268   $1,250.73   $1,250.75   $1,250.80