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	$110.65	9.119%	$120.7402	$120.74	$120.75	$120.70
Purchase #2	$167.89	13.461%	$190.4897	$190.49	$190.50	$190.50
Purchase #3	$180.40	8.715%	$196.1219	$196.12	$196.10	$196.10
Purchase #4	$173.75	11.183%	$193.1805	$193.18	$193.20	$193.20
Purchase #5	$134.45	3.624%	$139.3225	$139.32	$139.30	$139.30
Purchase #6	$26.81	7.753%	$28.8886	$28.89	$28.90	$28.90
Purchase #7	$19.29	7.648%	$20.7653	$20.77	$20.75	$20.80
7 purchase totals =	$813.24		$889.5087	$889.51	$889.50	$889.50