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	$10.74	8.556%	$11.6589	$11.66	$11.65	$11.70
Purchase #2	$99.69	5.871%	$105.5428	$105.54	$105.55	$105.50
Purchase #3	$107.44	3.735%	$111.4529	$111.45	$111.45	$111.50
Purchase #4	$146.49	13.313%	$165.9922	$165.99	$166.00	$166.00
Purchase #5	$245.84	10.131%	$270.7461	$270.75	$270.75	$270.70
Purchase #6	$158.48	4.535%	$165.6671	$165.67	$165.65	$165.70
Purchase #7	$17.53	3.661%	$18.1718	$18.17	$18.15	$18.20
7 purchase totals =	$786.21		$849.2318	$849.23	$849.20	$849.30