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	$72.49	9.150%	$79.1228	$79.12	$79.10	$79.10
Purchase #2	$179.73	4.827%	$188.4056	$188.41	$188.40	$188.40
Purchase #3	$129.33	6.379%	$137.58	$137.58	$137.60	$137.60
Purchase #4	$34.96	9.792%	$38.3833	$38.38	$38.40	$38.40
Purchase #5	$13.94	4.355%	$14.5471	$14.55	$14.55	$14.50
Purchase #6	$61.54	8.293%	$66.6435	$66.64	$66.65	$66.60
Purchase #7	$90.92	5.464%	$95.8879	$95.89	$95.90	$95.90
7 purchase totals =	$582.91		$620.5702	$620.57	$620.60	$620.50