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	$90.38	10.555%	$99.9196	$99.92	$99.90	$99.90
Purchase #2	$248.70	10.698%	$275.3059	$275.31	$275.30	$275.30
Purchase #3	$181.38	13.852%	$206.5048	$206.50	$206.50	$206.50
Purchase #4	$66.93	12.412%	$75.2374	$75.24	$75.25	$75.20
Purchase #5	$86.89	9.855%	$95.453	$95.45	$95.45	$95.50
Purchase #6	$74.74	9.576%	$81.8971	$81.90	$81.90	$81.90
Purchase #7	$127.45	3.488%	$131.8955	$131.90	$131.90	$131.90
7 purchase totals =	$876.47		$966.2133	$966.22	$966.20	$966.20