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	$160.93	4.770%	$168.6064	$168.61	$168.60	$168.60
Purchase #2	$12.36	4.235%	$12.8834	$12.88	$12.90	$12.90
Purchase #3	$155.30	10.690%	$171.9016	$171.90	$171.90	$171.90
Purchase #4	$80.34	10.504%	$88.7789	$88.78	$88.80	$88.80
Purchase #5	$40.69	3.525%	$42.1243	$42.12	$42.10	$42.10
Purchase #6	$39.29	3.522%	$40.6738	$40.67	$40.65	$40.70
Purchase #7	$8.98	8.286%	$9.7241	$9.72	$9.70	$9.70
7 purchase totals =	$497.89		$534.6925	$534.68	$534.65	$534.70