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	$76.52	3.103%	$78.8944	$78.89	$78.90	$78.90
Purchase #2	$50.70	3.782%	$52.6175	$52.62	$52.60	$52.60
Purchase #3	$212.26	9.538%	$232.5054	$232.51	$232.50	$232.50
Purchase #4	$155.77	6.343%	$165.6505	$165.65	$165.65	$165.70
Purchase #5	$54.31	13.123%	$61.4371	$61.44	$61.45	$61.40
Purchase #6	$236.79	4.469%	$247.3721	$247.37	$247.35	$247.40
Purchase #7	$61.54	8.459%	$66.7457	$66.75	$66.75	$66.70
7 purchase totals =	$847.89		$905.2227	$905.23	$905.20	$905.20