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	$80.58	10.807%	$89.2883	$89.29	$89.30	$89.30
Purchase #2	$64.69	12.853%	$73.0046	$73.00	$73.00	$73.00
Purchase #3	$119.73	10.635%	$132.4633	$132.46	$132.45	$132.50
Purchase #4	$79.29	12.573%	$89.2591	$89.26	$89.25	$89.30
Purchase #5	$60.65	7.236%	$65.0386	$65.04	$65.05	$65.00
Purchase #6	$151.79	3.344%	$156.8659	$156.87	$156.85	$156.90
Purchase #7	$185.65	6.345%	$197.4295	$197.43	$197.45	$197.40
7 purchase totals =	$742.38		$803.3493	$803.35	$803.35	$803.40