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	$221.59	12.776%	$249.9003	$249.90	$249.90	$249.90
Purchase #2	$146.45	8.661%	$159.134	$159.13	$159.15	$159.10
Purchase #3	$54.46	13.517%	$61.8214	$61.82	$61.80	$61.80
Purchase #4	$142.32	7.721%	$153.3085	$153.31	$153.30	$153.30
Purchase #5	$149.58	5.171%	$157.3148	$157.31	$157.30	$157.30
Purchase #6	$150.30	10.299%	$165.7794	$165.78	$165.80	$165.80
Purchase #7	$192.58	13.538%	$218.6515	$218.65	$218.65	$218.70
7 purchase totals =	$1,057.28		$1,165.9099	$1,165.90	$1,165.90	$1,165.90