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	$51.45	9.366%	$56.2688	$56.27	$56.25	$56.30
Purchase #2	$148.59	11.785%	$166.1013	$166.10	$166.10	$166.10
Purchase #3	$17.82	3.121%	$18.3762	$18.38	$18.40	$18.40
Purchase #4	$246.48	13.274%	$279.1978	$279.20	$279.20	$279.20
Purchase #5	$145.60	11.558%	$162.4284	$162.43	$162.45	$162.40
Purchase #6	$63.49	10.368%	$70.0726	$70.07	$70.05	$70.10
Purchase #7	$35.79	11.273%	$39.8246	$39.82	$39.80	$39.80
7 purchase totals =	$709.22		$792.2697	$792.27	$792.25	$792.30