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	$134.29	7.796%	$144.7592	$144.76	$144.75	$144.80
Purchase #2	$37.47	11.383%	$41.7352	$41.74	$41.75	$41.70
Purchase #3	$111.66	10.574%	$123.4669	$123.47	$123.45	$123.50
Purchase #4	$157.76	5.530%	$166.4841	$166.48	$166.50	$166.50
Purchase #5	$19.58	5.773%	$20.7104	$20.71	$20.70	$20.70
Purchase #6	$192.25	10.870%	$213.1476	$213.15	$213.15	$213.10
Purchase #7	$32.96	9.401%	$36.0586	$36.06	$36.05	$36.10
7 purchase totals =	$685.97		$746.3620	$746.37	$746.35	$746.40