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	$90.38	10.303%	$99.6919	$99.69	$99.70	$99.70
Purchase #2	$69.67	6.332%	$74.0815	$74.08	$74.10	$74.10
Purchase #3	$190.87	12.343%	$214.4291	$214.43	$214.45	$214.40
Purchase #4	$54.87	4.382%	$57.2744	$57.27	$57.25	$57.30
Purchase #5	$55.86	6.172%	$59.3077	$59.31	$59.30	$59.30
Purchase #6	$142.35	9.208%	$155.4576	$155.46	$155.45	$155.50
Purchase #7	$222.65	4.539%	$232.7561	$232.76	$232.75	$232.80
7 purchase totals =	$826.65		$892.9983	$893.00	$893.00	$893.10