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	$37.77	13.530%	$42.8803	$42.88	$42.90	$42.90
Purchase #2	$91.73	10.609%	$101.4616	$101.46	$101.45	$101.50
Purchase #3	$189.28	8.341%	$205.0678	$205.07	$205.05	$205.10
Purchase #4	$135.97	6.301%	$144.5375	$144.54	$144.55	$144.50
Purchase #5	$224.77	7.288%	$241.1512	$241.15	$241.15	$241.20
Purchase #6	$93.78	6.339%	$99.7247	$99.72	$99.70	$99.70
Purchase #7	$64.43	9.579%	$70.6017	$70.60	$70.60	$70.60
7 purchase totals =	$837.73		$905.4248	$905.42	$905.40	$905.50