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 $119.74   3.203%   $123.5753   $123.58   $123.60   $123.60  
  Purchase #2 $28.78   10.691%   $31.8569   $31.86   $31.85   $31.90  
  Purchase #3 $60.36   8.366%   $65.4097   $65.41   $65.40   $65.40  
  Purchase #4 $209.76   13.139%   $237.3204   $237.32   $237.30   $237.30  
  Purchase #5 $63.25   8.117%   $68.384   $68.38   $68.40   $68.40  
  Purchase #6 $203.73   10.113%   $224.3332   $224.33   $224.35   $224.30  
  Purchase #7 $7.99   7.716%   $8.6065   $8.61   $8.60   $8.60  
  7 purchase totals = $693.61       $759.4860   $759.49   $759.50   $759.50