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	$50.33	6.286%	$53.4937	$53.49	$53.50	$53.50
Purchase #2	$49.37	10.815%	$54.7094	$54.71	$54.70	$54.70
Purchase #3	$47.43	11.485%	$52.8773	$52.88	$52.90	$52.90
Purchase #4	$205.44	12.833%	$231.8041	$231.80	$231.80	$231.80
Purchase #5	$221.48	7.606%	$238.3258	$238.33	$238.35	$238.30
Purchase #6	$38.47	5.415%	$40.5532	$40.55	$40.55	$40.60
Purchase #7	$155.45	11.106%	$172.7143	$172.71	$172.70	$172.70
7 purchase totals =	$767.97		$844.4778	$844.47	$844.50	$844.50