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	$190.90	9.407%	$208.858	$208.86	$208.85	$208.90
Purchase #2	$23.63	5.347%	$24.8935	$24.89	$24.90	$24.90
Purchase #3	$103.58	11.202%	$115.183	$115.18	$115.20	$115.20
Purchase #4	$49.47	10.865%	$54.8449	$54.84	$54.85	$54.80
Purchase #5	$89.41	11.403%	$99.6054	$99.61	$99.60	$99.60
Purchase #6	$230.43	11.411%	$256.7244	$256.72	$256.70	$256.70
Purchase #7	$66.48	6.468%	$70.7799	$70.78	$70.80	$70.80
7 purchase totals =	$753.90		$830.8891	$830.88	$830.90	$830.90