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	$7.60	4.234%	$7.9218	$7.92	$7.90	$7.90
Purchase #2	$174.72	13.224%	$197.825	$197.83	$197.85	$197.80
Purchase #3	$68.82	11.179%	$76.5134	$76.51	$76.50	$76.50
Purchase #4	$45.87	5.737%	$48.5016	$48.50	$48.50	$48.50
Purchase #5	$50.65	9.694%	$55.56	$55.56	$55.55	$55.60
Purchase #6	$189.76	13.554%	$215.4801	$215.48	$215.50	$215.50
Purchase #7	$167.84	3.521%	$173.7496	$173.75	$173.75	$173.70
7 purchase totals =	$705.26		$775.5515	$775.55	$775.55	$775.50