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	$7.69	6.858%	$8.2174	$8.22	$8.20	$8.20
Purchase #2	$244.43	10.833%	$270.9091	$270.91	$270.90	$270.90
Purchase #3	$105.32	5.495%	$111.1073	$111.11	$111.10	$111.10
Purchase #4	$69.85	3.454%	$72.2626	$72.26	$72.25	$72.30
Purchase #5	$130.35	12.817%	$147.057	$147.06	$147.05	$147.10
Purchase #6	$60.75	5.821%	$64.2863	$64.29	$64.30	$64.30
Purchase #7	$121.33	13.395%	$137.5822	$137.58	$137.60	$137.60
7 purchase totals =	$739.72		$811.4219	$811.43	$811.40	$811.50