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	$146.52	13.165%	$165.8094	$165.81	$165.80	$165.80
Purchase #2	$59.52	5.501%	$62.7942	$62.79	$62.80	$62.80
Purchase #3	$144.94	9.586%	$158.8339	$158.83	$158.85	$158.80
Purchase #4	$150.91	10.164%	$166.2485	$166.25	$166.25	$166.20
Purchase #5	$167.53	4.398%	$174.898	$174.90	$174.90	$174.90
Purchase #6	$20.74	13.594%	$23.5594	$23.56	$23.55	$23.60
Purchase #7	$143.97	10.611%	$159.2467	$159.25	$159.25	$159.20
7 purchase totals =	$834.13		$911.3901	$911.39	$911.40	$911.30