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	$19.86	3.273%	$20.51	$20.51	$20.50	$20.50
Purchase #2	$22.86	7.753%	$24.6323	$24.63	$24.65	$24.60
Purchase #3	$39.84	7.341%	$42.7647	$42.76	$42.75	$42.80
Purchase #4	$157.76	5.335%	$166.1765	$166.18	$166.20	$166.20
Purchase #5	$150.30	13.385%	$170.4177	$170.42	$170.40	$170.40
Purchase #6	$14.63	6.443%	$15.5726	$15.57	$15.55	$15.60
Purchase #7	$57.55	5.231%	$60.5604	$60.56	$60.55	$60.60
7 purchase totals =	$462.80		$500.6342	$500.63	$500.60	$500.70