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	$100.98	7.457%	$108.5101	$108.51	$108.50	$108.50
Purchase #2	$77.49	10.453%	$85.59	$85.59	$85.60	$85.60
Purchase #3	$162.68	4.661%	$170.2625	$170.26	$170.25	$170.30
Purchase #4	$94.54	12.306%	$106.1741	$106.17	$106.15	$106.20
Purchase #5	$112.91	13.185%	$127.7972	$127.80	$127.80	$127.80
Purchase #6	$80.42	13.405%	$91.2003	$91.20	$91.20	$91.20
Purchase #7	$118.32	5.519%	$124.8501	$124.85	$124.85	$124.90
7 purchase totals =	$747.34		$814.3843	$814.38	$814.35	$814.50