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	$149.52	5.591%	$157.8797	$157.88	$157.90	$157.90
Purchase #2	$93.70	3.140%	$96.6422	$96.64	$96.65	$96.60
Purchase #3	$167.59	13.730%	$190.6001	$190.60	$190.60	$190.60
Purchase #4	$148.42	11.173%	$165.003	$165.00	$165.00	$165.00
Purchase #5	$29.51	3.104%	$30.426	$30.43	$30.45	$30.40
Purchase #6	$217.73	6.251%	$231.3403	$231.34	$231.35	$231.30
Purchase #7	$96.76	3.746%	$100.3846	$100.38	$100.40	$100.40
7 purchase totals =	$903.23		$972.2759	$972.27	$972.35	$972.20