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	$106.91	13.482%	$121.3236	$121.32	$121.30	$121.30
Purchase #2	$164.89	4.696%	$172.6332	$172.63	$172.65	$172.60
Purchase #3	$192.46	5.131%	$202.3351	$202.34	$202.35	$202.30
Purchase #4	$74.46	8.112%	$80.5002	$80.50	$80.50	$80.50
Purchase #5	$157.64	9.446%	$172.5307	$172.53	$172.55	$172.50
Purchase #6	$54.53	13.353%	$61.8114	$61.81	$61.80	$61.80
Purchase #7	$68.57	13.757%	$78.0032	$78.00	$78.00	$78.00
7 purchase totals =	$819.46		$889.1374	$889.13	$889.15	$889.00