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	$17.82	4.776%	$18.6711	$18.67	$18.65	$18.70
Purchase #2	$42.96	4.354%	$44.8305	$44.83	$44.85	$44.80
Purchase #3	$111.85	13.498%	$126.9475	$126.95	$126.95	$126.90
Purchase #4	$17.48	8.115%	$18.8985	$18.90	$18.90	$18.90
Purchase #5	$172.27	9.710%	$188.9974	$189.00	$189.00	$189.00
Purchase #6	$77.63	5.800%	$82.1325	$82.13	$82.15	$82.10
Purchase #7	$243.32	5.194%	$255.958	$255.96	$255.95	$256.00
7 purchase totals =	$683.33		$736.4355	$736.44	$736.45	$736.40