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 $206.44   7.518%   $221.9602   $221.96   $221.95   $222.00  
  Purchase #2 $75.97   13.401%   $86.1507   $86.15   $86.15   $86.20  
  Purchase #3 $168.93   5.621%   $178.4256   $178.43   $178.45   $178.40  
  Purchase #4 $245.32   11.743%   $274.1279   $274.13   $274.15   $274.10  
  Purchase #5 $178.39   3.411%   $184.4749   $184.47   $184.45   $184.50  
  Purchase #6 $163.73   12.362%   $183.9703   $183.97   $183.95   $184.00  
  Purchase #7 $85.36   3.443%   $88.2989   $88.30   $88.30   $88.30  
  7 purchase totals = $1,124.14       $1,217.4085   $1,217.41   $1,217.40   $1,217.50