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	$30.95	6.386%	$32.9265	$32.93	$32.95	$32.90
Purchase #2	$80.37	6.116%	$85.2854	$85.29	$85.30	$85.30
Purchase #3	$65.42	13.143%	$74.0182	$74.02	$74.00	$74.00
Purchase #4	$150.48	8.110%	$162.6839	$162.68	$162.70	$162.70
Purchase #5	$29.79	9.228%	$32.539	$32.54	$32.55	$32.50
Purchase #6	$226.91	5.254%	$238.8319	$238.83	$238.85	$238.80
Purchase #7	$43.70	3.103%	$45.056	$45.06	$45.05	$45.10
7 purchase totals =	$627.62		$671.3409	$671.35	$671.40	$671.30