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	$111.94	13.549%	$127.1068	$127.11	$127.10	$127.10
Purchase #2	$139.88	10.771%	$154.9465	$154.95	$154.95	$154.90
Purchase #3	$16.89	11.168%	$18.7763	$18.78	$18.80	$18.80
Purchase #4	$121.87	10.614%	$134.8053	$134.81	$134.80	$134.80
Purchase #5	$248.56	13.354%	$281.7527	$281.75	$281.75	$281.80
Purchase #6	$19.25	4.815%	$20.1769	$20.18	$20.20	$20.20
Purchase #7	$175.81	8.133%	$190.1086	$190.11	$190.10	$190.10
7 purchase totals =	$834.20		$927.6731	$927.69	$927.70	$927.70