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 $202.47   7.176%   $216.9992   $217.00   $217.00   $217.00  
  Purchase #2 $68.81   7.546%   $74.0024   $74.00   $74.00   $74.00  
  Purchase #3 $60.68   5.176%   $63.8208   $63.82   $63.80   $63.80  
  Purchase #4 $165.92   5.318%   $174.7436   $174.74   $174.75   $174.70  
  Purchase #5 $162.67   9.489%   $178.1058   $178.11   $178.10   $178.10  
  Purchase #6 $72.84   5.293%   $76.6954   $76.70   $76.70   $76.70  
  Purchase #7 $19.36   4.389%   $20.2097   $20.21   $20.20   $20.20  
  7 purchase totals = $752.75       $804.5769   $804.58   $804.55   $804.50