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	$39.74	6.467%	$42.31	$42.31	$42.30	$42.30
Purchase #2	$122.92	11.769%	$137.3865	$137.39	$137.40	$137.40
Purchase #3	$139.72	13.819%	$159.0279	$159.03	$159.05	$159.00
Purchase #4	$118.79	8.132%	$128.45	$128.45	$128.45	$128.50
Purchase #5	$63.62	5.191%	$66.9225	$66.92	$66.90	$66.90
Purchase #6	$177.30	8.306%	$192.0265	$192.03	$192.05	$192.00
Purchase #7	$53.64	13.382%	$60.8181	$60.82	$60.80	$60.80
7 purchase totals =	$715.73		$786.9415	$786.95	$786.95	$786.90