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	$37.56	9.158%	$40.9997	$41.00	$41.00	$41.00
Purchase #2	$102.93	5.212%	$108.2947	$108.29	$108.30	$108.30
Purchase #3	$18.85	8.831%	$20.5146	$20.51	$20.50	$20.50
Purchase #4	$39.80	13.558%	$45.1961	$45.20	$45.20	$45.20
Purchase #5	$21.55	4.160%	$22.4465	$22.45	$22.45	$22.40
Purchase #6	$141.83	10.611%	$156.8796	$156.88	$156.90	$156.90
Purchase #7	$37.69	7.731%	$40.6038	$40.60	$40.60	$40.60
7 purchase totals =	$400.21		$434.9350	$434.93	$434.95	$434.90