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	$33.25	12.495%	$37.4046	$37.40	$37.40	$37.40
Purchase #2	$6.86	8.189%	$7.4218	$7.42	$7.40	$7.40
Purchase #3	$95.71	9.386%	$104.6933	$104.69	$104.70	$104.70
Purchase #4	$153.47	11.738%	$171.4843	$171.48	$171.50	$171.50
Purchase #5	$127.55	13.755%	$145.0945	$145.09	$145.10	$145.10
Purchase #6	$38.28	8.549%	$41.5526	$41.55	$41.55	$41.60
Purchase #7	$154.49	11.154%	$171.7218	$171.72	$171.70	$171.70
7 purchase totals =	$609.61		$679.3729	$679.35	$679.35	$679.40