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	$122.74	12.537%	$138.1279	$138.13	$138.15	$138.10
Purchase #2	$20.74	4.764%	$21.7281	$21.73	$21.75	$21.70
Purchase #3	$39.79	7.801%	$42.894	$42.89	$42.90	$42.90
Purchase #4	$149.90	12.471%	$168.594	$168.59	$168.60	$168.60
Purchase #5	$36.95	13.359%	$41.8862	$41.89	$41.90	$41.90
Purchase #6	$145.27	9.708%	$159.3728	$159.37	$159.35	$159.40
Purchase #7	$230.83	7.339%	$247.7706	$247.77	$247.75	$247.80
7 purchase totals =	$746.22		$820.3736	$820.37	$820.40	$820.40