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	$151.61	5.555%	$160.0319	$160.03	$160.05	$160.00
Purchase #2	$112.42	9.615%	$123.2292	$123.23	$123.25	$123.20
Purchase #3	$57.96	6.710%	$61.8491	$61.85	$61.85	$61.80
Purchase #4	$99.37	10.141%	$109.4471	$109.45	$109.45	$109.40
Purchase #5	$93.76	8.149%	$101.4005	$101.40	$101.40	$101.40
Purchase #6	$233.96	9.488%	$256.1581	$256.16	$256.15	$256.20
Purchase #7	$164.55	9.196%	$179.682	$179.68	$179.70	$179.70
7 purchase totals =	$913.63		$991.7979	$991.80	$991.85	$991.70