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	$155.39	3.224%	$160.3998	$160.40	$160.40	$160.40
Purchase #2	$217.69	7.251%	$233.4747	$233.47	$233.45	$233.50
Purchase #3	$146.53	7.330%	$157.2706	$157.27	$157.25	$157.30
Purchase #4	$14.96	3.748%	$15.5207	$15.52	$15.50	$15.50
Purchase #5	$66.62	7.152%	$71.3847	$71.38	$71.40	$71.40
Purchase #6	$19.47	9.280%	$21.2768	$21.28	$21.30	$21.30
Purchase #7	$230.77	6.124%	$244.9024	$244.90	$244.90	$244.90
7 purchase totals =	$851.43		$904.2297	$904.22	$904.20	$904.30