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	$40.75	12.235%	$45.7358	$45.74	$45.75	$45.70
Purchase #2	$33.49	12.196%	$37.5744	$37.57	$37.55	$37.60
Purchase #3	$182.28	13.163%	$206.2735	$206.27	$206.25	$206.30
Purchase #4	$128.50	5.283%	$135.2887	$135.29	$135.30	$135.30
Purchase #5	$207.47	10.397%	$229.0407	$229.04	$229.05	$229.00
Purchase #6	$139.98	11.715%	$156.3787	$156.38	$156.40	$156.40
Purchase #7	$113.56	12.581%	$127.847	$127.85	$127.85	$127.80
7 purchase totals =	$846.03		$938.1388	$938.14	$938.15	$938.10