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	$159.39	4.447%	$166.4781	$166.48	$166.50	$166.50
Purchase #2	$224.79	9.393%	$245.9045	$245.90	$245.90	$245.90
Purchase #3	$57.83	6.373%	$61.5155	$61.52	$61.50	$61.50
Purchase #4	$149.77	10.343%	$165.2607	$165.26	$165.25	$165.30
Purchase #5	$37.95	7.717%	$40.8786	$40.88	$40.90	$40.90
Purchase #6	$127.50	7.797%	$137.4412	$137.44	$137.45	$137.40
Purchase #7	$184.33	3.237%	$190.2968	$190.30	$190.30	$190.30
7 purchase totals =	$941.56		$1,007.7754	$1,007.78	$1,007.80	$1,007.80