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	$5.88	11.364%	$6.5482	$6.55	$6.55	$6.50
Purchase #2	$51.92	5.680%	$54.8691	$54.87	$54.85	$54.90
Purchase #3	$152.56	4.305%	$159.1277	$159.13	$159.15	$159.10
Purchase #4	$26.59	4.848%	$27.8791	$27.88	$27.90	$27.90
Purchase #5	$154.88	12.198%	$173.7723	$173.77	$173.75	$173.80
Purchase #6	$112.27	13.140%	$127.0223	$127.02	$127.00	$127.00
Purchase #7	$233.89	13.616%	$265.7365	$265.74	$265.75	$265.70
7 purchase totals =	$737.99		$814.9552	$814.96	$814.95	$814.90