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	$110.62	7.453%	$118.8645	$118.86	$118.85	$118.90
Purchase #2	$128.94	11.168%	$143.34	$143.34	$143.35	$143.30
Purchase #3	$15.39	13.446%	$17.4593	$17.46	$17.45	$17.50
Purchase #4	$80.32	6.405%	$85.4645	$85.46	$85.45	$85.50
Purchase #5	$141.83	5.669%	$149.8703	$149.87	$149.85	$149.90
Purchase #6	$47.51	7.107%	$50.8865	$50.89	$50.90	$50.90
Purchase #7	$46.27	6.577%	$49.3132	$49.31	$49.30	$49.30
7 purchase totals =	$570.88		$615.1983	$615.19	$615.15	$615.30