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	$103.78	8.702%	$112.8109	$112.81	$112.80	$112.80
Purchase #2	$97.46	13.544%	$110.66	$110.66	$110.65	$110.70
Purchase #3	$93.92	5.828%	$99.3937	$99.39	$99.40	$99.40
Purchase #4	$219.35	10.713%	$242.849	$242.85	$242.85	$242.80
Purchase #5	$212.82	7.182%	$228.1047	$228.10	$228.10	$228.10
Purchase #6	$60.81	6.158%	$64.5547	$64.55	$64.55	$64.60
Purchase #7	$128.71	12.433%	$144.7125	$144.71	$144.70	$144.70
7 purchase totals =	$916.85		$1,003.0855	$1,003.07	$1,003.05	$1,003.10