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	$75.77	12.756%	$85.4352	$85.44	$85.45	$85.40
Purchase #2	$142.93	10.810%	$158.3807	$158.38	$158.40	$158.40
Purchase #3	$69.98	10.434%	$77.2817	$77.28	$77.30	$77.30
Purchase #4	$154.56	6.700%	$164.9155	$164.92	$164.90	$164.90
Purchase #5	$188.58	5.754%	$199.4309	$199.43	$199.45	$199.40
Purchase #6	$181.65	11.539%	$202.6106	$202.61	$202.60	$202.60
Purchase #7	$37.63	12.230%	$42.2321	$42.23	$42.25	$42.20
7 purchase totals =	$851.10		$930.2867	$930.29	$930.35	$930.20