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	$142.91	11.297%	$159.0545	$159.05	$159.05	$159.10
Purchase #2	$116.28	9.564%	$127.401	$127.40	$127.40	$127.40
Purchase #3	$77.52	3.707%	$80.3937	$80.39	$80.40	$80.40
Purchase #4	$219.75	9.619%	$240.8878	$240.89	$240.90	$240.90
Purchase #5	$49.37	8.795%	$53.7121	$53.71	$53.70	$53.70
Purchase #6	$159.37	3.141%	$164.3758	$164.38	$164.40	$164.40
Purchase #7	$25.39	3.462%	$26.269	$26.27	$26.25	$26.30
7 purchase totals =	$790.59		$852.0939	$852.09	$852.10	$852.20