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	$33.99	11.705%	$37.9685	$37.97	$37.95	$38.00
Purchase #2	$124.76	5.242%	$131.2999	$131.30	$131.30	$131.30
Purchase #3	$172.34	7.636%	$185.4999	$185.50	$185.50	$185.50
Purchase #4	$56.41	4.750%	$59.0895	$59.09	$59.10	$59.10
Purchase #5	$77.86	13.204%	$88.1406	$88.14	$88.15	$88.10
Purchase #6	$15.81	13.725%	$17.9799	$17.98	$18.00	$18.00
Purchase #7	$179.61	5.707%	$189.8603	$189.86	$189.85	$189.90
7 purchase totals =	$660.78		$709.8386	$709.84	$709.85	$709.90