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	$24.48	12.430%	$27.5229	$27.52	$27.50	$27.50
Purchase #2	$189.83	8.458%	$205.8858	$205.89	$205.90	$205.90
Purchase #3	$237.25	11.765%	$265.1625	$265.16	$265.15	$265.20
Purchase #4	$128.80	11.724%	$143.9005	$143.90	$143.90	$143.90
Purchase #5	$63.98	5.468%	$67.4784	$67.48	$67.50	$67.50
Purchase #6	$85.77	5.798%	$90.7429	$90.74	$90.75	$90.70
Purchase #7	$25.59	11.673%	$28.5771	$28.58	$28.60	$28.60
7 purchase totals =	$755.70		$829.2701	$829.27	$829.30	$829.30