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	$202.55	10.539%	$223.8967	$223.90	$223.90	$223.90
Purchase #2	$152.54	13.639%	$173.3449	$173.34	$173.35	$173.30
Purchase #3	$66.39	9.374%	$72.6134	$72.61	$72.60	$72.60
Purchase #4	$143.62	5.866%	$152.0447	$152.04	$152.05	$152.00
Purchase #5	$221.82	12.235%	$248.9597	$248.96	$248.95	$249.00
Purchase #6	$46.82	8.705%	$50.8957	$50.90	$50.90	$50.90
Purchase #7	$5.41	12.270%	$6.0738	$6.07	$6.05	$6.10
7 purchase totals =	$839.15		$927.8289	$927.82	$927.80	$927.80