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	$98.98	4.161%	$103.0986	$103.10	$103.10	$103.10
Purchase #2	$188.46	4.699%	$197.3157	$197.32	$197.30	$197.30
Purchase #3	$165.94	5.799%	$175.5629	$175.56	$175.55	$175.60
Purchase #4	$244.66	12.561%	$275.3917	$275.39	$275.40	$275.40
Purchase #5	$101.48	9.763%	$111.3875	$111.39	$111.40	$111.40
Purchase #6	$120.69	13.115%	$136.5185	$136.52	$136.50	$136.50
Purchase #7	$87.37	13.182%	$98.8871	$98.89	$98.90	$98.90
7 purchase totals =	$1,007.58		$1,098.1620	$1,098.17	$1,098.15	$1,098.20