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	$140.30	4.217%	$146.2165	$146.22	$146.20	$146.20
Purchase #2	$172.37	7.764%	$185.7528	$185.75	$185.75	$185.80
Purchase #3	$211.33	8.272%	$228.8112	$228.81	$228.80	$228.80
Purchase #4	$238.74	10.422%	$263.6215	$263.62	$263.60	$263.60
Purchase #5	$160.90	3.140%	$165.9523	$165.95	$165.95	$166.00
Purchase #6	$42.85	7.214%	$45.9412	$45.94	$45.95	$45.90
Purchase #7	$225.40	7.726%	$242.8144	$242.81	$242.80	$242.80
7 purchase totals =	$1,191.89		$1,279.1099	$1,279.10	$1,279.05	$1,279.10