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	$15.89	4.502%	$16.6054	$16.61	$16.60	$16.60
Purchase #2	$131.54	11.576%	$146.7671	$146.77	$146.75	$146.80
Purchase #3	$28.28	13.252%	$32.0277	$32.03	$32.05	$32.00
Purchase #4	$229.29	10.569%	$253.5237	$253.52	$253.50	$253.50
Purchase #5	$150.96	11.657%	$168.5574	$168.56	$168.55	$168.60
Purchase #6	$111.51	8.299%	$120.7642	$120.76	$120.75	$120.80
Purchase #7	$65.43	6.279%	$69.5383	$69.54	$69.55	$69.50
7 purchase totals =	$732.90		$807.7838	$807.79	$807.75	$807.80