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	$66.52	4.714%	$69.6558	$69.66	$69.65	$69.70
Purchase #2	$89.59	10.706%	$99.1815	$99.18	$99.20	$99.20
Purchase #3	$89.63	10.189%	$98.7624	$98.76	$98.75	$98.80
Purchase #4	$137.71	7.167%	$147.5797	$147.58	$147.60	$147.60
Purchase #5	$123.25	4.855%	$129.2338	$129.23	$129.25	$129.20
Purchase #6	$93.27	13.458%	$105.8223	$105.82	$105.80	$105.80
Purchase #7	$61.59	6.395%	$65.5287	$65.53	$65.55	$65.50
7 purchase totals =	$661.56		$715.7642	$715.76	$715.80	$715.80