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	$80.75	11.358%	$89.9216	$89.92	$89.90	$89.90
Purchase #2	$130.86	11.117%	$145.4077	$145.41	$145.40	$145.40
Purchase #3	$208.39	5.200%	$219.2263	$219.23	$219.25	$219.20
Purchase #4	$36.88	13.153%	$41.7308	$41.73	$41.75	$41.70
Purchase #5	$16.35	3.291%	$16.8881	$16.89	$16.90	$16.90
Purchase #6	$146.60	8.378%	$158.8821	$158.88	$158.90	$158.90
Purchase #7	$162.70	11.468%	$181.3584	$181.36	$181.35	$181.40
7 purchase totals =	$782.53		$853.4150	$853.42	$853.45	$853.40