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	$175.65	7.550%	$188.9116	$188.91	$188.90	$188.90
Purchase #2	$139.39	3.711%	$144.5628	$144.56	$144.55	$144.60
Purchase #3	$155.43	6.312%	$165.2407	$165.24	$165.25	$165.20
Purchase #4	$141.50	7.188%	$151.671	$151.67	$151.65	$151.70
Purchase #5	$222.52	12.456%	$250.2371	$250.24	$250.25	$250.20
Purchase #6	$45.32	9.822%	$49.7713	$49.77	$49.75	$49.80
Purchase #7	$220.40	4.562%	$230.4546	$230.45	$230.45	$230.50
7 purchase totals =	$1,100.21		$1,180.8491	$1,180.84	$1,180.80	$1,180.90