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	$199.79	3.745%	$207.2721	$207.27	$207.25	$207.30
Purchase #2	$129.47	12.858%	$146.1173	$146.12	$146.10	$146.10
Purchase #3	$192.78	13.226%	$218.2771	$218.28	$218.30	$218.30
Purchase #4	$52.59	12.390%	$59.1059	$59.11	$59.10	$59.10
Purchase #5	$128.62	11.526%	$143.4447	$143.44	$143.45	$143.40
Purchase #6	$27.73	13.637%	$31.5115	$31.51	$31.50	$31.50
Purchase #7	$95.72	6.760%	$102.1907	$102.19	$102.20	$102.20
7 purchase totals =	$826.70		$907.9193	$907.92	$907.90	$907.90