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	$101.58	13.512%	$115.3055	$115.31	$115.30	$115.30
Purchase #2	$26.42	6.610%	$28.1664	$28.17	$28.15	$28.20
Purchase #3	$129.27	11.337%	$143.9253	$143.93	$143.95	$143.90
Purchase #4	$163.47	5.482%	$172.4314	$172.43	$172.45	$172.40
Purchase #5	$205.44	12.744%	$231.6213	$231.62	$231.60	$231.60
Purchase #6	$56.88	4.779%	$59.5983	$59.60	$59.60	$59.60
Purchase #7	$167.55	7.618%	$180.314	$180.31	$180.30	$180.30
7 purchase totals =	$850.61		$931.3622	$931.37	$931.35	$931.30