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	$236.40	4.758%	$247.6479	$247.65	$247.65	$247.60
Purchase #2	$115.84	9.448%	$126.7846	$126.78	$126.80	$126.80
Purchase #3	$242.63	11.237%	$269.8943	$269.89	$269.90	$269.90
Purchase #4	$229.48	11.174%	$255.1221	$255.12	$255.10	$255.10
Purchase #5	$85.49	4.264%	$89.1353	$89.14	$89.15	$89.10
Purchase #6	$112.52	4.362%	$117.4281	$117.43	$117.45	$117.40
Purchase #7	$32.58	3.313%	$33.6594	$33.66	$33.65	$33.70
7 purchase totals =	$1,054.94		$1,139.6717	$1,139.67	$1,139.70	$1,139.60