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	$102.42	5.261%	$107.8083	$107.81	$107.80	$107.80
Purchase #2	$172.57	9.686%	$189.2851	$189.29	$189.30	$189.30
Purchase #3	$88.69	12.123%	$99.4419	$99.44	$99.45	$99.40
Purchase #4	$29.90	11.376%	$33.3014	$33.30	$33.30	$33.30
Purchase #5	$13.98	13.770%	$15.905	$15.91	$15.90	$15.90
Purchase #6	$166.84	10.590%	$184.5084	$184.51	$184.50	$184.50
Purchase #7	$58.67	6.103%	$62.2506	$62.25	$62.25	$62.30
7 purchase totals =	$633.07		$692.5007	$692.51	$692.50	$692.50