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	$205.59	8.659%	$223.392	$223.39	$223.40	$223.40
Purchase #2	$18.38	4.185%	$19.1492	$19.15	$19.15	$19.10
Purchase #3	$109.99	13.455%	$124.7892	$124.79	$124.80	$124.80
Purchase #4	$22.75	6.176%	$24.155	$24.16	$24.15	$24.20
Purchase #5	$77.77	12.256%	$87.3015	$87.30	$87.30	$87.30
Purchase #6	$180.86	8.583%	$196.3832	$196.38	$196.40	$196.40
Purchase #7	$62.91	3.516%	$65.1219	$65.12	$65.10	$65.10
7 purchase totals =	$678.25		$740.2920	$740.29	$740.30	$740.30