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 $236.41   4.145%   $246.2092   $246.21   $246.20   $246.20  
  Purchase #2 $89.57   3.674%   $92.8608   $92.86   $92.85   $92.90  
  Purchase #3 $230.34   3.388%   $238.1439   $238.14   $238.15   $238.10  
  Purchase #4 $146.63   8.181%   $158.6258   $158.63   $158.65   $158.60  
  Purchase #5 $189.34   4.238%   $197.3642   $197.36   $197.35   $197.40  
  Purchase #6 $118.96   4.793%   $124.6618   $124.66   $124.65   $124.70  
  Purchase #7 $162.40   7.420%   $174.4501   $174.45   $174.45   $174.50  
  7 purchase totals = $1,173.65       $1,232.3158   $1,232.31   $1,232.30   $1,232.40