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	$116.33	3.603%	$120.5214	$120.52	$120.50	$120.50
Purchase #2	$70.62	11.427%	$78.6897	$78.69	$78.70	$78.70
Purchase #3	$168.89	13.120%	$191.0484	$191.05	$191.05	$191.00
Purchase #4	$151.85	7.797%	$163.6897	$163.69	$163.70	$163.70
Purchase #5	$168.78	4.538%	$176.4392	$176.44	$176.45	$176.40
Purchase #6	$224.57	12.401%	$252.4189	$252.42	$252.40	$252.40
Purchase #7	$159.29	5.780%	$168.497	$168.50	$168.50	$168.50
7 purchase totals =	$1,060.33		$1,151.3043	$1,151.31	$1,151.30	$1,151.20