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	$131.75	9.666%	$144.485	$144.49	$144.50	$144.50
Purchase #2	$40.55	5.345%	$42.7174	$42.72	$42.70	$42.70
Purchase #3	$203.29	10.277%	$224.1821	$224.18	$224.20	$224.20
Purchase #4	$61.62	3.691%	$63.8944	$63.89	$63.90	$63.90
Purchase #5	$122.44	6.476%	$130.3692	$130.37	$130.35	$130.40
Purchase #6	$189.26	3.807%	$196.4651	$196.47	$196.45	$196.50
Purchase #7	$32.27	5.770%	$34.132	$34.13	$34.15	$34.10
7 purchase totals =	$781.18		$836.2452	$836.25	$836.25	$836.30