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	$129.69	10.480%	$143.2815	$143.28	$143.30	$143.30
Purchase #2	$56.33	11.151%	$62.6114	$62.61	$62.60	$62.60
Purchase #3	$199.74	7.128%	$213.9775	$213.98	$214.00	$214.00
Purchase #4	$130.42	13.760%	$148.3658	$148.37	$148.35	$148.40
Purchase #5	$80.58	11.293%	$89.6799	$89.68	$89.70	$89.70
Purchase #6	$78.66	12.527%	$88.5137	$88.51	$88.50	$88.50
Purchase #7	$100.98	8.690%	$109.7552	$109.76	$109.75	$109.80
7 purchase totals =	$776.40		$856.1850	$856.19	$856.20	$856.30