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	$15.56	6.177%	$16.5211	$16.52	$16.50	$16.50
Purchase #2	$66.75	8.744%	$72.5866	$72.59	$72.60	$72.60
Purchase #3	$159.42	13.115%	$180.3279	$180.33	$180.35	$180.30
Purchase #4	$153.47	13.526%	$174.2284	$174.23	$174.25	$174.20
Purchase #5	$95.35	4.147%	$99.3042	$99.30	$99.30	$99.30
Purchase #6	$134.96	13.761%	$153.5318	$153.53	$153.55	$153.50
Purchase #7	$48.31	7.849%	$52.1019	$52.10	$52.10	$52.10
7 purchase totals =	$673.82		$748.6019	$748.60	$748.65	$748.50