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	$53.66	10.400%	$59.2406	$59.24	$59.25	$59.20
Purchase #2	$163.52	12.222%	$183.5054	$183.51	$183.50	$183.50
Purchase #3	$41.45	11.468%	$46.2035	$46.20	$46.20	$46.20
Purchase #4	$153.92	10.195%	$169.6121	$169.61	$169.60	$169.60
Purchase #5	$194.86	13.532%	$221.2285	$221.23	$221.25	$221.20
Purchase #6	$20.93	6.731%	$22.3388	$22.34	$22.35	$22.30
Purchase #7	$185.85	13.778%	$211.4564	$211.46	$211.45	$211.50
7 purchase totals =	$814.19		$913.5853	$913.59	$913.60	$913.50