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	$59.93	13.429%	$67.978	$67.98	$68.00	$68.00
Purchase #2	$114.37	11.150%	$127.1223	$127.12	$127.10	$127.10
Purchase #3	$95.71	13.786%	$108.9046	$108.90	$108.90	$108.90
Purchase #4	$112.48	3.736%	$116.6823	$116.68	$116.70	$116.70
Purchase #5	$205.88	6.477%	$219.2148	$219.21	$219.20	$219.20
Purchase #6	$218.69	4.110%	$227.6782	$227.68	$227.70	$227.70
Purchase #7	$63.50	12.255%	$71.2819	$71.28	$71.30	$71.30
7 purchase totals =	$870.56		$938.8621	$938.85	$938.90	$938.90