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 $228.94   11.271%   $254.7438   $254.74   $254.75   $254.70  
  Purchase #2 $68.44   12.177%   $76.7739   $76.77   $76.75   $76.80  
  Purchase #3 $150.43   12.282%   $168.9058   $168.91   $168.90   $168.90  
  Purchase #4 $175.96   13.152%   $199.1023   $199.10   $199.10   $199.10  
  Purchase #5 $180.85   8.770%   $196.7105   $196.71   $196.70   $196.70  
  Purchase #6 $233.54   12.807%   $263.4495   $263.45   $263.45   $263.40  
  Purchase #7 $140.73   7.112%   $150.7387   $150.74   $150.75   $150.70  
  7 purchase totals = $1,178.89       $1,310.4245   $1,310.42   $1,310.40   $1,310.30