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	$5.57	6.296%	$5.9207	$5.92	$5.90	$5.90
Purchase #2	$39.96	3.509%	$41.3622	$41.36	$41.35	$41.40
Purchase #3	$123.32	3.371%	$127.4771	$127.48	$127.50	$127.50
Purchase #4	$218.75	11.186%	$243.2194	$243.22	$243.20	$243.20
Purchase #5	$166.63	3.234%	$172.0188	$172.02	$172.00	$172.00
Purchase #6	$77.71	7.168%	$83.2803	$83.28	$83.30	$83.30
Purchase #7	$229.89	8.564%	$249.5778	$249.58	$249.60	$249.60
7 purchase totals =	$861.83		$922.8563	$922.86	$922.85	$922.90