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	$237.30	13.156%	$268.5192	$268.52	$268.50	$268.50
Purchase #2	$42.98	13.155%	$48.634	$48.63	$48.65	$48.60
Purchase #3	$16.59	5.402%	$17.4862	$17.49	$17.50	$17.50
Purchase #4	$72.56	13.113%	$82.0748	$82.07	$82.05	$82.10
Purchase #5	$12.63	8.522%	$13.7063	$13.71	$13.70	$13.70
Purchase #6	$208.43	7.504%	$224.0706	$224.07	$224.05	$224.10
Purchase #7	$40.48	12.590%	$45.5764	$45.58	$45.60	$45.60
7 purchase totals =	$630.97		$700.0675	$700.07	$700.05	$700.10