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	$25.59	10.528%	$28.2841	$28.28	$28.30	$28.30
Purchase #2	$196.43	11.717%	$219.4457	$219.45	$219.45	$219.40
Purchase #3	$218.29	13.396%	$247.5321	$247.53	$247.55	$247.50
Purchase #4	$97.46	4.853%	$102.1897	$102.19	$102.20	$102.20
Purchase #5	$131.95	10.462%	$145.7546	$145.75	$145.75	$145.80
Purchase #6	$78.82	13.707%	$89.6239	$89.62	$89.60	$89.60
Purchase #7	$101.71	3.867%	$105.6431	$105.64	$105.65	$105.60
7 purchase totals =	$850.25		$938.4732	$938.46	$938.50	$938.40