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	$136.26	6.755%	$145.4644	$145.46	$145.45	$145.50
Purchase #2	$171.91	7.846%	$185.3981	$185.40	$185.40	$185.40
Purchase #3	$175.51	3.461%	$181.5844	$181.58	$181.60	$181.60
Purchase #4	$37.47	4.429%	$39.1295	$39.13	$39.15	$39.10
Purchase #5	$62.76	3.400%	$64.8938	$64.89	$64.90	$64.90
Purchase #6	$76.75	4.495%	$80.1999	$80.20	$80.20	$80.20
Purchase #7	$181.48	4.586%	$189.8027	$189.80	$189.80	$189.80
7 purchase totals =	$842.14		$886.4728	$886.46	$886.50	$886.50