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	$87.57	11.373%	$97.5293	$97.53	$97.55	$97.50
Purchase #2	$45.31	13.510%	$51.4314	$51.43	$51.45	$51.40
Purchase #3	$50.31	10.513%	$55.5991	$55.60	$55.60	$55.60
Purchase #4	$74.85	5.835%	$79.2175	$79.22	$79.20	$79.20
Purchase #5	$85.35	4.730%	$89.3871	$89.39	$89.40	$89.40
Purchase #6	$35.73	5.225%	$37.5969	$37.60	$37.60	$37.60
Purchase #7	$165.96	8.171%	$179.5206	$179.52	$179.50	$179.50
7 purchase totals =	$545.08		$590.2819	$590.29	$590.30	$590.20