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	$133.39	11.559%	$148.8086	$148.81	$148.80	$148.80
Purchase #2	$133.87	8.723%	$145.5475	$145.55	$145.55	$145.50
Purchase #3	$166.30	7.799%	$179.2697	$179.27	$179.25	$179.30
Purchase #4	$19.87	12.660%	$22.3855	$22.39	$22.40	$22.40
Purchase #5	$166.59	13.652%	$189.3329	$189.33	$189.35	$189.30
Purchase #6	$80.30	6.506%	$85.5243	$85.52	$85.50	$85.50
Purchase #7	$41.72	10.196%	$45.9738	$45.97	$45.95	$46.00
7 purchase totals =	$742.04		$816.8423	$816.84	$816.80	$816.80