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 $170.37   5.719%   $180.1135   $180.11   $180.10   $180.10  
  Purchase #2 $99.63   8.201%   $107.8007   $107.80   $107.80   $107.80  
  Purchase #3 $239.84   6.828%   $256.2163   $256.22   $256.20   $256.20  
  Purchase #4 $71.70   10.141%   $78.9711   $78.97   $78.95   $79.00  
  Purchase #5 $199.33   8.594%   $216.4604   $216.46   $216.45   $216.50  
  Purchase #6 $247.69   13.163%   $280.2934   $280.29   $280.30   $280.30  
  Purchase #7 $53.40   12.614%   $60.1359   $60.14   $60.15   $60.10  
  7 purchase totals = $1,081.96       $1,179.9913   $1,179.99   $1,179.95   $1,180.00