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	$51.25	5.403%	$54.019	$54.02	$54.00	$54.00
Purchase #2	$141.35	3.459%	$146.2393	$146.24	$146.25	$146.20
Purchase #3	$17.29	5.199%	$18.1889	$18.19	$18.20	$18.20
Purchase #4	$105.92	5.144%	$111.3685	$111.37	$111.35	$111.40
Purchase #5	$22.72	12.324%	$25.52	$25.52	$25.50	$25.50
Purchase #6	$48.30	6.859%	$51.6129	$51.61	$51.60	$51.60
Purchase #7	$101.64	6.528%	$108.2751	$108.28	$108.30	$108.30
7 purchase totals =	$488.47		$515.2237	$515.23	$515.20	$515.20