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 $226.54   6.472%   $241.2017   $241.20   $241.20   $241.20  
  Purchase #2 $187.67   11.337%   $208.9461   $208.95   $208.95   $208.90  
  Purchase #3 $104.78   8.743%   $113.9409   $113.94   $113.95   $113.90  
  Purchase #4 $60.46   9.522%   $66.217   $66.22   $66.20   $66.20  
  Purchase #5 $42.48   4.116%   $44.2285   $44.23   $44.25   $44.20  
  Purchase #6 $32.63   9.507%   $35.7321   $35.73   $35.75   $35.70  
  Purchase #7 $145.27   13.523%   $164.9149   $164.91   $164.90   $164.90  
  7 purchase totals = $799.83       $875.1812   $875.18   $875.20   $875.00