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	$57.49	8.393%	$62.3151	$62.32	$62.30	$62.30
Purchase #2	$65.99	9.423%	$72.2082	$72.21	$72.20	$72.20
Purchase #3	$201.48	10.619%	$222.8752	$222.88	$222.90	$222.90
Purchase #4	$75.48	8.492%	$81.8898	$81.89	$81.90	$81.90
Purchase #5	$144.96	13.184%	$164.0715	$164.07	$164.05	$164.10
Purchase #6	$133.41	5.640%	$140.9343	$140.93	$140.95	$140.90
Purchase #7	$32.41	10.184%	$35.7106	$35.71	$35.70	$35.70
7 purchase totals =	$711.22		$780.0047	$780.01	$780.00	$780.00