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	$90.63	10.637%	$100.2703	$100.27	$100.25	$100.30
Purchase #2	$183.69	13.338%	$208.1906	$208.19	$208.20	$208.20
Purchase #3	$143.37	13.331%	$162.4827	$162.48	$162.50	$162.50
Purchase #4	$127.87	13.739%	$145.4381	$145.44	$145.45	$145.40
Purchase #5	$172.74	6.693%	$184.3015	$184.30	$184.30	$184.30
Purchase #6	$219.68	4.196%	$228.8978	$228.90	$228.90	$228.90
Purchase #7	$151.28	11.648%	$168.9011	$168.90	$168.90	$168.90
7 purchase totals =	$1,089.26		$1,198.4821	$1,198.48	$1,198.50	$1,198.50