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	$33.97	11.230%	$37.7848	$37.78	$37.80	$37.80
Purchase #2	$193.72	10.506%	$214.0722	$214.07	$214.05	$214.10
Purchase #3	$90.86	10.470%	$100.373	$100.37	$100.35	$100.40
Purchase #4	$114.87	13.320%	$130.1707	$130.17	$130.15	$130.20
Purchase #5	$98.47	7.867%	$106.2166	$106.22	$106.20	$106.20
Purchase #6	$188.43	10.827%	$208.8313	$208.83	$208.85	$208.80
Purchase #7	$75.45	10.384%	$83.2847	$83.28	$83.30	$83.30
7 purchase totals =	$795.77		$880.7333	$880.72	$880.70	$880.80