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	$241.45	12.354%	$271.2787	$271.28	$271.30	$271.30
Purchase #2	$11.39	13.142%	$12.8869	$12.89	$12.90	$12.90
Purchase #3	$76.27	7.779%	$82.203	$82.20	$82.20	$82.20
Purchase #4	$177.56	7.510%	$190.8948	$190.89	$190.90	$190.90
Purchase #5	$197.43	12.567%	$222.241	$222.24	$222.25	$222.20
Purchase #6	$70.26	5.107%	$73.8482	$73.85	$73.85	$73.80
Purchase #7	$70.41	7.114%	$75.419	$75.42	$75.40	$75.40
7 purchase totals =	$844.77		$928.7716	$928.77	$928.80	$928.70