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	$139.26	12.389%	$156.5129	$156.51	$156.50	$156.50
Purchase #2	$18.35	12.497%	$20.6432	$20.64	$20.65	$20.60
Purchase #3	$52.59	7.732%	$56.6563	$56.66	$56.65	$56.70
Purchase #4	$52.78	4.664%	$55.2417	$55.24	$55.25	$55.20
Purchase #5	$75.64	12.447%	$85.0549	$85.05	$85.05	$85.10
Purchase #6	$220.93	7.661%	$237.8554	$237.86	$237.85	$237.90
Purchase #7	$41.35	9.692%	$45.3576	$45.36	$45.35	$45.40
7 purchase totals =	$600.90		$657.3220	$657.32	$657.30	$657.40