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	$211.52	10.824%	$234.4149	$234.41	$234.40	$234.40
Purchase #2	$86.66	3.583%	$89.765	$89.77	$89.75	$89.80
Purchase #3	$77.28	13.259%	$87.5266	$87.53	$87.55	$87.50
Purchase #4	$30.56	6.685%	$32.6029	$32.60	$32.60	$32.60
Purchase #5	$162.42	10.747%	$179.8753	$179.88	$179.90	$179.90
Purchase #6	$170.88	13.486%	$193.9249	$193.92	$193.90	$193.90
Purchase #7	$159.75	13.772%	$181.7508	$181.75	$181.75	$181.80
7 purchase totals =	$899.07		$999.8604	$999.86	$999.85	$999.90