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	$147.34	12.266%	$165.4127	$165.41	$165.40	$165.40
Purchase #2	$112.67	4.425%	$117.6556	$117.66	$117.65	$117.70
Purchase #3	$151.87	6.570%	$161.8479	$161.85	$161.85	$161.80
Purchase #4	$111.92	3.217%	$115.5205	$115.52	$115.50	$115.50
Purchase #5	$78.71	13.550%	$89.3752	$89.38	$89.40	$89.40
Purchase #6	$183.38	9.467%	$200.7406	$200.74	$200.75	$200.70
Purchase #7	$66.43	6.145%	$70.5121	$70.51	$70.50	$70.50
7 purchase totals =	$852.32		$921.0646	$921.07	$921.05	$921.00