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	$55.43	8.234%	$59.9941	$59.99	$60.00	$60.00
Purchase #2	$35.84	12.398%	$40.2834	$40.28	$40.30	$40.30
Purchase #3	$99.52	12.323%	$111.7838	$111.78	$111.80	$111.80
Purchase #4	$11.95	4.118%	$12.4421	$12.44	$12.45	$12.40
Purchase #5	$6.89	10.505%	$7.6138	$7.61	$7.60	$7.60
Purchase #6	$81.64	10.197%	$89.9648	$89.96	$89.95	$90.00
Purchase #7	$231.44	9.506%	$253.4407	$253.44	$253.45	$253.40
7 purchase totals =	$522.71		$575.5227	$575.50	$575.55	$575.50