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 $105.61   7.166%   $113.178   $113.18   $113.20   $113.20  
  Purchase #2 $158.44   13.632%   $180.0385   $180.04   $180.05   $180.00  
  Purchase #3 $250.53   9.351%   $273.9571   $273.96   $273.95   $274.00  
  Purchase #4 $219.29   13.665%   $249.256   $249.26   $249.25   $249.30  
  Purchase #5 $155.44   10.284%   $171.4254   $171.43   $171.45   $171.40  
  Purchase #6 $136.49   9.147%   $148.9747   $148.97   $148.95   $149.00  
  Purchase #7 $118.96   10.488%   $131.4365   $131.44   $131.45   $131.40  
  7 purchase totals = $1,144.76       $1,268.2662   $1,268.28   $1,268.30   $1,268.30