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	$18.91	12.733%	$21.3178	$21.32	$21.30	$21.30
Purchase #2	$142.34	6.390%	$151.4355	$151.44	$151.45	$151.40
Purchase #3	$206.57	9.572%	$226.3429	$226.34	$226.35	$226.30
Purchase #4	$56.52	4.397%	$59.0052	$59.01	$59.00	$59.00
Purchase #5	$212.26	13.360%	$240.6179	$240.62	$240.60	$240.60
Purchase #6	$49.81	5.202%	$52.4011	$52.40	$52.40	$52.40
Purchase #7	$158.80	8.667%	$172.5632	$172.56	$172.55	$172.60
7 purchase totals =	$845.21		$923.6836	$923.69	$923.65	$923.60