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	$17.90	4.500%	$18.7055	$18.71	$18.70	$18.70
Purchase #2	$238.76	7.576%	$256.8485	$256.85	$256.85	$256.80
Purchase #3	$226.35	7.660%	$243.6884	$243.69	$243.70	$243.70
Purchase #4	$69.39	12.643%	$78.163	$78.16	$78.15	$78.20
Purchase #5	$153.39	4.759%	$160.6898	$160.69	$160.70	$160.70
Purchase #6	$234.82	4.243%	$244.7834	$244.78	$244.80	$244.80
Purchase #7	$134.35	7.517%	$144.4491	$144.45	$144.45	$144.40
7 purchase totals =	$1,074.96		$1,147.3277	$1,147.33	$1,147.35	$1,147.30