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	$40.93	3.688%	$42.4395	$42.44	$42.45	$42.40
Purchase #2	$146.44	4.722%	$153.3549	$153.35	$153.35	$153.40
Purchase #3	$87.91	12.670%	$99.0482	$99.05	$99.05	$99.00
Purchase #4	$173.51	5.267%	$182.6488	$182.65	$182.65	$182.60
Purchase #5	$223.26	8.690%	$242.6613	$242.66	$242.65	$242.70
Purchase #6	$196.42	12.751%	$221.4655	$221.47	$221.45	$221.50
Purchase #7	$34.58	7.678%	$37.2351	$37.24	$37.25	$37.20
7 purchase totals =	$903.05		$978.8533	$978.86	$978.85	$978.80