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 $153.26   10.143%   $168.8052   $168.81   $168.80   $168.80  
  Purchase #2 $229.93   8.344%   $249.1154   $249.12   $249.10   $249.10  
  Purchase #3 $158.42   11.309%   $176.3357   $176.34   $176.35   $176.30  
  Purchase #4 $230.67   4.863%   $241.8875   $241.89   $241.90   $241.90  
  Purchase #5 $184.94   12.414%   $207.8985   $207.90   $207.90   $207.90  
  Purchase #6 $239.48   7.434%   $257.2829   $257.28   $257.30   $257.30  
  Purchase #7 $244.56   6.368%   $260.1336   $260.13   $260.15   $260.10  
  7 purchase totals = $1,441.26       $1,561.4588   $1,561.47   $1,561.50   $1,561.40