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	$31.94	4.173%	$33.2729	$33.27	$33.25	$33.30
Purchase #2	$132.54	11.873%	$148.2765	$148.28	$148.30	$148.30
Purchase #3	$98.78	10.738%	$109.387	$109.39	$109.40	$109.40
Purchase #4	$231.35	8.251%	$250.4387	$250.44	$250.45	$250.40
Purchase #5	$66.54	13.670%	$75.636	$75.64	$75.65	$75.60
Purchase #6	$149.58	5.515%	$157.8293	$157.83	$157.85	$157.80
Purchase #7	$184.90	10.331%	$204.002	$204.00	$204.00	$204.00
7 purchase totals =	$895.63		$978.8424	$978.85	$978.90	$978.80