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	$170.95	5.390%	$180.1642	$180.16	$180.15	$180.20
Purchase #2	$134.95	7.796%	$145.4707	$145.47	$145.45	$145.50
Purchase #3	$42.72	3.293%	$44.1268	$44.13	$44.15	$44.10
Purchase #4	$210.91	7.774%	$227.3061	$227.31	$227.30	$227.30
Purchase #5	$88.40	13.130%	$100.0069	$100.01	$100.00	$100.00
Purchase #6	$136.63	13.332%	$154.8455	$154.85	$154.85	$154.80
Purchase #7	$232.96	10.702%	$257.8914	$257.89	$257.90	$257.90
7 purchase totals =	$1,017.52		$1,109.8116	$1,109.82	$1,109.80	$1,109.80