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	$161.95	5.340%	$170.5981	$170.60	$170.60	$170.60
Purchase #2	$214.45	4.661%	$224.4455	$224.45	$224.45	$224.40
Purchase #3	$105.96	5.245%	$111.5176	$111.52	$111.50	$111.50
Purchase #4	$85.53	3.871%	$88.8409	$88.84	$88.85	$88.80
Purchase #5	$89.61	3.842%	$93.0528	$93.05	$93.05	$93.10
Purchase #6	$57.79	3.254%	$59.6705	$59.67	$59.65	$59.70
Purchase #7	$146.89	12.410%	$165.119	$165.12	$165.10	$165.10
7 purchase totals =	$862.18		$913.2444	$913.25	$913.20	$913.20