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	$159.88	4.250%	$166.6749	$166.67	$166.65	$166.70
Purchase #2	$22.51	11.181%	$25.0268	$25.03	$25.05	$25.00
Purchase #3	$165.44	3.758%	$171.6572	$171.66	$171.65	$171.70
Purchase #4	$101.98	9.288%	$111.4519	$111.45	$111.45	$111.50
Purchase #5	$194.39	3.594%	$201.3764	$201.38	$201.40	$201.40
Purchase #6	$40.78	4.563%	$42.6408	$42.64	$42.65	$42.60
Purchase #7	$243.40	7.363%	$261.3215	$261.32	$261.30	$261.30
7 purchase totals =	$928.38		$980.1495	$980.15	$980.15	$980.20