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	$53.27	11.863%	$59.5894	$59.59	$59.60	$59.60
Purchase #2	$225.40	3.630%	$233.582	$233.58	$233.60	$233.60
Purchase #3	$28.66	7.431%	$30.7897	$30.79	$30.80	$30.80
Purchase #4	$82.64	5.780%	$87.4166	$87.42	$87.40	$87.40
Purchase #5	$229.54	10.250%	$253.0679	$253.07	$253.05	$253.10
Purchase #6	$244.39	10.837%	$270.8745	$270.87	$270.85	$270.90
Purchase #7	$39.96	13.313%	$45.2799	$45.28	$45.30	$45.30
7 purchase totals =	$903.86		$980.6000	$980.60	$980.60	$980.70