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	$237.33	6.652%	$253.1172	$253.12	$253.10	$253.10
Purchase #2	$28.91	11.658%	$32.2803	$32.28	$32.30	$32.30
Purchase #3	$35.62	5.593%	$37.6122	$37.61	$37.60	$37.60
Purchase #4	$190.78	7.660%	$205.3937	$205.39	$205.40	$205.40
Purchase #5	$237.29	13.520%	$269.3716	$269.37	$269.35	$269.40
Purchase #6	$33.27	5.873%	$35.2239	$35.22	$35.20	$35.20
Purchase #7	$245.27	13.867%	$279.2816	$279.28	$279.30	$279.30
7 purchase totals =	$1,008.47		$1,112.2805	$1,112.27	$1,112.25	$1,112.30