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	$115.69	8.816%	$125.8892	$125.89	$125.90	$125.90
Purchase #2	$85.61	6.701%	$91.3467	$91.35	$91.35	$91.30
Purchase #3	$197.43	9.215%	$215.6232	$215.62	$215.60	$215.60
Purchase #4	$56.40	9.633%	$61.833	$61.83	$61.85	$61.80
Purchase #5	$161.40	7.117%	$172.8868	$172.89	$172.90	$172.90
Purchase #6	$131.72	4.468%	$137.6052	$137.61	$137.60	$137.60
Purchase #7	$101.65	8.303%	$110.09	$110.09	$110.10	$110.10
7 purchase totals =	$849.90		$915.2741	$915.28	$915.30	$915.20