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 $34.68   3.620%   $35.9354   $35.94   $35.95   $35.90  
  Purchase #2 $140.64   13.544%   $159.6883   $159.69   $159.70   $159.70  
  Purchase #3 $165.26   12.131%   $185.3077   $185.31   $185.30   $185.30  
  Purchase #4 $38.62   11.148%   $42.9254   $42.93   $42.95   $42.90  
  Purchase #5 $116.54   8.532%   $126.4832   $126.48   $126.50   $126.50  
  Purchase #6 $247.64   3.845%   $257.1618   $257.16   $257.15   $257.20  
  Purchase #7 $214.41   12.227%   $240.6259   $240.63   $240.65   $240.60  
  7 purchase totals = $957.79       $1,048.1277   $1,048.14   $1,048.20   $1,048.10