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	$141.38	6.397%	$150.4241	$150.42	$150.40	$150.40
Purchase #2	$77.96	9.436%	$85.3163	$85.32	$85.30	$85.30
Purchase #3	$249.47	10.616%	$275.9537	$275.95	$275.95	$276.00
Purchase #4	$24.58	8.182%	$26.5911	$26.59	$26.60	$26.60
Purchase #5	$145.54	5.305%	$153.2609	$153.26	$153.25	$153.30
Purchase #6	$150.52	9.807%	$165.2815	$165.28	$165.30	$165.30
Purchase #7	$218.68	4.495%	$228.5097	$228.51	$228.50	$228.50
7 purchase totals =	$1,008.13		$1,085.3373	$1,085.33	$1,085.30	$1,085.40