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	$19.76	7.723%	$21.2861	$21.29	$21.30	$21.30
Purchase #2	$204.66	6.280%	$217.5126	$217.51	$217.50	$217.50
Purchase #3	$47.27	7.418%	$50.7765	$50.78	$50.80	$50.80
Purchase #4	$141.82	7.103%	$151.8935	$151.89	$151.90	$151.90
Purchase #5	$100.90	5.380%	$106.3284	$106.33	$106.35	$106.30
Purchase #6	$173.65	13.689%	$197.4209	$197.42	$197.40	$197.40
Purchase #7	$119.27	9.220%	$130.2667	$130.27	$130.25	$130.30
7 purchase totals =	$807.33		$875.4847	$875.49	$875.50	$875.50