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 $223.38   5.838%   $236.4209   $236.42   $236.40   $236.40  
  Purchase #2 $178.42   8.708%   $193.9568   $193.96   $193.95   $194.00  
  Purchase #3 $114.61   9.829%   $125.875   $125.88   $125.90   $125.90  
  Purchase #4 $165.36   6.733%   $176.4937   $176.49   $176.50   $176.50  
  Purchase #5 $56.45   3.105%   $58.2028   $58.20   $58.20   $58.20  
  Purchase #6 $205.25   9.467%   $224.681   $224.68   $224.70   $224.70  
  Purchase #7 $201.63   12.469%   $226.7712   $226.77   $226.75   $226.80  
  7 purchase totals = $1,145.10       $1,242.4014   $1,242.40   $1,242.40   $1,242.50