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	$63.54	11.614%	$70.9195	$70.92	$70.90	$70.90
Purchase #2	$102.79	5.526%	$108.4702	$108.47	$108.45	$108.50
Purchase #3	$212.99	9.574%	$233.3817	$233.38	$233.40	$233.40
Purchase #4	$59.58	9.181%	$65.05	$65.05	$65.05	$65.10
Purchase #5	$79.74	8.414%	$86.4493	$86.45	$86.45	$86.40
Purchase #6	$249.55	10.413%	$275.5356	$275.54	$275.55	$275.50
Purchase #7	$45.89	3.723%	$47.5985	$47.60	$47.60	$47.60
7 purchase totals =	$814.08		$887.4048	$887.41	$887.40	$887.40