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	$67.89	5.157%	$71.3911	$71.39	$71.40	$71.40
Purchase #2	$223.92	8.204%	$242.2904	$242.29	$242.30	$242.30
Purchase #3	$192.68	6.633%	$205.4605	$205.46	$205.45	$205.50
Purchase #4	$105.77	6.707%	$112.864	$112.86	$112.85	$112.90
Purchase #5	$58.65	10.810%	$64.9901	$64.99	$65.00	$65.00
Purchase #6	$250.56	3.124%	$258.3875	$258.39	$258.40	$258.40
Purchase #7	$244.34	8.827%	$265.9079	$265.91	$265.90	$265.90
7 purchase totals =	$1,143.81		$1,221.2915	$1,221.29	$1,221.30	$1,221.40