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	$105.96	6.555%	$112.9057	$112.91	$112.90	$112.90
Purchase #2	$201.27	8.587%	$218.5531	$218.55	$218.55	$218.60
Purchase #3	$248.74	13.344%	$281.9319	$281.93	$281.95	$281.90
Purchase #4	$111.56	5.856%	$118.093	$118.09	$118.10	$118.10
Purchase #5	$63.66	7.418%	$68.3823	$68.38	$68.40	$68.40
Purchase #6	$87.48	3.316%	$90.3808	$90.38	$90.40	$90.40
Purchase #7	$95.65	9.371%	$104.6134	$104.61	$104.60	$104.60
7 purchase totals =	$914.32		$994.8602	$994.85	$994.90	$994.90