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	$77.27	7.831%	$83.321	$83.32	$83.30	$83.30
Purchase #2	$139.85	13.457%	$158.6696	$158.67	$158.65	$158.70
Purchase #3	$144.27	5.702%	$152.4963	$152.50	$152.50	$152.50
Purchase #4	$87.57	10.154%	$96.4619	$96.46	$96.45	$96.50
Purchase #5	$7.36	5.375%	$7.7556	$7.76	$7.75	$7.80
Purchase #6	$200.75	4.343%	$209.4686	$209.47	$209.45	$209.50
Purchase #7	$30.70	10.222%	$33.8382	$33.84	$33.85	$33.80
7 purchase totals =	$687.77		$742.0112	$742.02	$741.95	$742.10