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	$67.83	8.326%	$73.4775	$73.48	$73.50	$73.50
Purchase #2	$127.45	4.406%	$133.0654	$133.07	$133.05	$133.10
Purchase #3	$213.88	4.507%	$223.5196	$223.52	$223.50	$223.50
Purchase #4	$50.50	4.730%	$52.8887	$52.89	$52.90	$52.90
Purchase #5	$139.82	6.319%	$148.6552	$148.66	$148.65	$148.70
Purchase #6	$54.89	10.686%	$60.7555	$60.76	$60.75	$60.80
Purchase #7	$47.34	4.294%	$49.3728	$49.37	$49.35	$49.40
7 purchase totals =	$701.71		$741.7347	$741.75	$741.70	$741.90