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	$35.40	4.450%	$36.9753	$36.98	$37.00	$37.00
Purchase #2	$19.26	4.112%	$20.052	$20.05	$20.05	$20.10
Purchase #3	$127.32	10.235%	$140.3512	$140.35	$140.35	$140.40
Purchase #4	$74.97	3.817%	$77.8316	$77.83	$77.85	$77.80
Purchase #5	$141.39	13.363%	$160.2839	$160.28	$160.30	$160.30
Purchase #6	$136.27	9.331%	$148.9854	$148.99	$149.00	$149.00
Purchase #7	$76.29	8.517%	$82.7876	$82.79	$82.80	$82.80
7 purchase totals =	$610.90		$667.2670	$667.27	$667.35	$667.40