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	$122.34	7.526%	$131.5473	$131.55	$131.55	$131.50
Purchase #2	$61.83	3.637%	$64.0788	$64.08	$64.10	$64.10
Purchase #3	$243.74	8.772%	$265.1209	$265.12	$265.10	$265.10
Purchase #4	$36.64	6.847%	$39.1487	$39.15	$39.15	$39.10
Purchase #5	$111.52	10.399%	$123.117	$123.12	$123.10	$123.10
Purchase #6	$155.68	13.591%	$176.8385	$176.84	$176.85	$176.80
Purchase #7	$88.51	3.490%	$91.599	$91.60	$91.60	$91.60
7 purchase totals =	$820.26		$891.4502	$891.46	$891.45	$891.30