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	$31.94	6.286%	$33.9477	$33.95	$33.95	$33.90
Purchase #2	$108.83	13.538%	$123.5634	$123.56	$123.55	$123.60
Purchase #3	$202.56	13.567%	$230.0413	$230.04	$230.05	$230.00
Purchase #4	$78.47	5.192%	$82.5442	$82.54	$82.55	$82.50
Purchase #5	$221.41	8.129%	$239.4084	$239.41	$239.40	$239.40
Purchase #6	$108.40	8.505%	$117.6194	$117.62	$117.60	$117.60
Purchase #7	$19.96	3.108%	$20.5804	$20.58	$20.60	$20.60
7 purchase totals =	$771.57		$847.7048	$847.70	$847.70	$847.60