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	$11.45	8.191%	$12.3879	$12.39	$12.40	$12.40
Purchase #2	$54.91	13.726%	$62.4469	$62.45	$62.45	$62.40
Purchase #3	$240.91	13.750%	$274.0351	$274.04	$274.05	$274.00
Purchase #4	$67.39	6.120%	$71.5143	$71.51	$71.50	$71.50
Purchase #5	$99.34	5.401%	$104.7054	$104.71	$104.70	$104.70
Purchase #6	$63.84	12.176%	$71.6132	$71.61	$71.60	$71.60
Purchase #7	$93.62	12.444%	$105.2701	$105.27	$105.25	$105.30
7 purchase totals =	$631.46		$701.9729	$701.98	$701.95	$701.90