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	$143.93	12.197%	$161.4851	$161.49	$161.50	$161.50
Purchase #2	$74.81	11.435%	$83.3645	$83.36	$83.35	$83.40
Purchase #3	$59.42	10.151%	$65.4517	$65.45	$65.45	$65.50
Purchase #4	$56.40	8.802%	$61.3643	$61.36	$61.35	$61.40
Purchase #5	$104.77	6.120%	$111.1819	$111.18	$111.20	$111.20
Purchase #6	$98.81	10.843%	$109.524	$109.52	$109.50	$109.50
Purchase #7	$213.35	12.387%	$239.7777	$239.78	$239.80	$239.80
7 purchase totals =	$751.49		$832.1492	$832.14	$832.15	$832.30