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	$95.52	5.512%	$100.7851	$100.79	$100.80	$100.80
Purchase #2	$6.70	13.326%	$7.5928	$7.59	$7.60	$7.60
Purchase #3	$246.27	7.192%	$263.9817	$263.98	$264.00	$264.00
Purchase #4	$15.40	13.225%	$17.4367	$17.44	$17.45	$17.40
Purchase #5	$176.38	5.372%	$185.8551	$185.86	$185.85	$185.90
Purchase #6	$91.43	8.707%	$99.3908	$99.39	$99.40	$99.40
Purchase #7	$66.64	12.372%	$74.8847	$74.88	$74.90	$74.90
7 purchase totals =	$698.34		$749.9269	$749.93	$750.00	$750.00