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	$100.98	13.480%	$114.5921	$114.59	$114.60	$114.60
Purchase #2	$58.38	13.637%	$66.3413	$66.34	$66.35	$66.30
Purchase #3	$82.29	8.439%	$89.2345	$89.23	$89.25	$89.20
Purchase #4	$46.72	12.333%	$52.482	$52.48	$52.50	$52.50
Purchase #5	$180.31	5.182%	$189.6537	$189.65	$189.65	$189.70
Purchase #6	$77.54	11.821%	$86.706	$86.71	$86.70	$86.70
Purchase #7	$113.54	13.275%	$128.6124	$128.61	$128.60	$128.60
7 purchase totals =	$659.76		$727.6220	$727.61	$727.65	$727.60