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	$107.73	3.196%	$111.1731	$111.17	$111.15	$111.20
Purchase #2	$235.58	4.123%	$245.293	$245.29	$245.30	$245.30
Purchase #3	$88.52	3.341%	$91.4775	$91.48	$91.50	$91.50
Purchase #4	$235.81	8.696%	$256.316	$256.32	$256.30	$256.30
Purchase #5	$92.93	5.213%	$97.7744	$97.77	$97.75	$97.80
Purchase #6	$241.89	13.741%	$275.1281	$275.13	$275.15	$275.10
Purchase #7	$196.47	13.632%	$223.2528	$223.25	$223.25	$223.30
7 purchase totals =	$1,198.93		$1,300.4149	$1,300.41	$1,300.40	$1,300.50