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	$116.56	5.778%	$123.2948	$123.29	$123.30	$123.30
Purchase #2	$40.34	6.813%	$43.0884	$43.09	$43.10	$43.10
Purchase #3	$60.83	9.730%	$66.7488	$66.75	$66.75	$66.70
Purchase #4	$169.32	5.872%	$179.2625	$179.26	$179.25	$179.30
Purchase #5	$52.41	4.607%	$54.8245	$54.82	$54.80	$54.80
Purchase #6	$222.25	10.848%	$246.3597	$246.36	$246.35	$246.40
Purchase #7	$26.98	4.480%	$28.1887	$28.19	$28.20	$28.20
7 purchase totals =	$688.69		$741.7674	$741.76	$741.75	$741.80