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	$118.83	10.172%	$130.9174	$130.92	$130.90	$130.90
Purchase #2	$169.32	7.425%	$181.892	$181.89	$181.90	$181.90
Purchase #3	$36.56	3.618%	$37.8827	$37.88	$37.90	$37.90
Purchase #4	$194.29	5.781%	$205.5219	$205.52	$205.50	$205.50
Purchase #5	$193.64	11.492%	$215.8931	$215.89	$215.90	$215.90
Purchase #6	$48.78	9.103%	$53.2204	$53.22	$53.20	$53.20
Purchase #7	$12.85	4.761%	$13.4618	$13.46	$13.45	$13.50
7 purchase totals =	$774.27		$838.7893	$838.78	$838.75	$838.80