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	$76.29	11.725%	$85.235	$85.24	$85.25	$85.20
Purchase #2	$102.46	9.819%	$112.5205	$112.52	$112.50	$112.50
Purchase #3	$77.58	10.558%	$85.7709	$85.77	$85.75	$85.80
Purchase #4	$105.83	4.230%	$110.3066	$110.31	$110.30	$110.30
Purchase #5	$143.50	11.435%	$159.9092	$159.91	$159.90	$159.90
Purchase #6	$97.73	13.174%	$110.605	$110.61	$110.60	$110.60
Purchase #7	$38.47	3.718%	$39.9003	$39.90	$39.90	$39.90
7 purchase totals =	$641.86		$704.2475	$704.26	$704.20	$704.20