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	$61.28	13.224%	$69.3837	$69.38	$69.40	$69.40
Purchase #2	$205.86	12.474%	$231.539	$231.54	$231.55	$231.50
Purchase #3	$79.84	13.807%	$90.8635	$90.86	$90.85	$90.90
Purchase #4	$100.73	10.108%	$110.9118	$110.91	$110.90	$110.90
Purchase #5	$163.52	5.451%	$172.4335	$172.43	$172.45	$172.40
Purchase #6	$32.66	4.309%	$34.0673	$34.07	$34.05	$34.10
Purchase #7	$235.73	7.874%	$254.2914	$254.29	$254.30	$254.30
7 purchase totals =	$879.62		$963.4902	$963.48	$963.50	$963.50