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	$85.72	5.769%	$90.6652	$90.67	$90.65	$90.70
Purchase #2	$81.66	4.408%	$85.2596	$85.26	$85.25	$85.30
Purchase #3	$52.61	5.274%	$55.3847	$55.38	$55.40	$55.40
Purchase #4	$59.40	6.825%	$63.4541	$63.45	$63.45	$63.50
Purchase #5	$206.84	13.559%	$234.8854	$234.89	$234.90	$234.90
Purchase #6	$30.56	7.431%	$32.8309	$32.83	$32.85	$32.80
Purchase #7	$151.29	6.841%	$161.6397	$161.64	$161.65	$161.60
7 purchase totals =	$668.08		$724.1196	$724.12	$724.15	$724.20