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	$93.36	4.336%	$97.4081	$97.41	$97.40	$97.40
Purchase #2	$225.85	10.462%	$249.4784	$249.48	$249.50	$249.50
Purchase #3	$105.25	5.679%	$111.2271	$111.23	$111.25	$111.20
Purchase #4	$201.86	10.382%	$222.8171	$222.82	$222.80	$222.80
Purchase #5	$225.29	3.647%	$233.5063	$233.51	$233.50	$233.50
Purchase #6	$138.38	10.428%	$152.8103	$152.81	$152.80	$152.80
Purchase #7	$149.41	11.492%	$166.5802	$166.58	$166.60	$166.60
7 purchase totals =	$1,139.40		$1,233.8275	$1,233.84	$1,233.85	$1,233.80