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	$155.93	6.790%	$166.5176	$166.52	$166.50	$166.50
Purchase #2	$249.32	9.421%	$272.8084	$272.81	$272.80	$272.80
Purchase #3	$188.98	13.673%	$214.8192	$214.82	$214.80	$214.80
Purchase #4	$189.68	5.684%	$200.4614	$200.46	$200.45	$200.50
Purchase #5	$130.94	11.376%	$145.8357	$145.84	$145.85	$145.80
Purchase #6	$92.41	8.127%	$99.9202	$99.92	$99.90	$99.90
Purchase #7	$238.75	13.629%	$271.2892	$271.29	$271.30	$271.30
7 purchase totals =	$1,246.01		$1,371.6517	$1,371.66	$1,371.60	$1,371.60