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	$243.89	4.652%	$255.2358	$255.24	$255.25	$255.20
Purchase #2	$49.35	8.430%	$53.5102	$53.51	$53.50	$53.50
Purchase #3	$157.80	6.133%	$167.4779	$167.48	$167.50	$167.50
Purchase #4	$226.65	13.851%	$258.0433	$258.04	$258.05	$258.00
Purchase #5	$238.82	5.460%	$251.8596	$251.86	$251.85	$251.90
Purchase #6	$28.64	3.423%	$29.6203	$29.62	$29.60	$29.60
Purchase #7	$59.95	7.763%	$64.6039	$64.60	$64.60	$64.60
7 purchase totals =	$1,005.10		$1,080.3510	$1,080.35	$1,080.35	$1,080.30