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	$194.47	13.222%	$220.1828	$220.18	$220.20	$220.20
Purchase #2	$80.57	9.476%	$88.2048	$88.20	$88.20	$88.20
Purchase #3	$65.97	10.104%	$72.6356	$72.64	$72.65	$72.60
Purchase #4	$238.58	13.414%	$270.5831	$270.58	$270.60	$270.60
Purchase #5	$103.43	8.233%	$111.9454	$111.95	$111.95	$111.90
Purchase #6	$144.46	3.551%	$149.5898	$149.59	$149.60	$149.60
Purchase #7	$71.69	9.607%	$78.5773	$78.58	$78.60	$78.60
7 purchase totals =	$899.17		$991.7188	$991.72	$991.80	$991.70