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	$65.71	10.657%	$72.7127	$72.71	$72.70	$72.70
Purchase #2	$54.90	13.686%	$62.4136	$62.41	$62.40	$62.40
Purchase #3	$138.86	8.327%	$150.4229	$150.42	$150.40	$150.40
Purchase #4	$244.82	4.173%	$255.0363	$255.04	$255.05	$255.00
Purchase #5	$174.37	6.224%	$185.2228	$185.22	$185.20	$185.20
Purchase #6	$101.37	10.432%	$111.9449	$111.94	$111.95	$111.90
Purchase #7	$120.83	13.610%	$137.275	$137.28	$137.30	$137.30
7 purchase totals =	$900.86		$975.0282	$975.02	$975.00	$974.90