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	$135.94	10.163%	$149.7556	$149.76	$149.75	$149.80
Purchase #2	$37.62	13.200%	$42.5858	$42.59	$42.60	$42.60
Purchase #3	$219.54	8.498%	$238.1965	$238.20	$238.20	$238.20
Purchase #4	$19.51	10.306%	$21.5207	$21.52	$21.50	$21.50
Purchase #5	$147.77	5.644%	$156.1101	$156.11	$156.10	$156.10
Purchase #6	$180.47	4.339%	$188.3006	$188.30	$188.30	$188.30
Purchase #7	$38.27	10.604%	$42.3282	$42.33	$42.35	$42.30
7 purchase totals =	$779.12		$838.7975	$838.81	$838.80	$838.80