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	$30.56	3.167%	$31.5278	$31.53	$31.55	$31.50
Purchase #2	$47.97	4.306%	$50.0356	$50.04	$50.05	$50.00
Purchase #3	$91.42	10.384%	$100.9131	$100.91	$100.90	$100.90
Purchase #4	$80.83	8.232%	$87.4839	$87.48	$87.50	$87.50
Purchase #5	$99.69	6.481%	$106.1509	$106.15	$106.15	$106.20
Purchase #6	$14.51	6.332%	$15.4288	$15.43	$15.45	$15.40
Purchase #7	$234.34	9.523%	$256.6562	$256.66	$256.65	$256.70
7 purchase totals =	$599.32		$648.1963	$648.20	$648.25	$648.20