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	$36.99	3.516%	$38.2906	$38.29	$38.30	$38.30
Purchase #2	$134.52	13.266%	$152.3654	$152.37	$152.35	$152.40
Purchase #3	$87.81	3.782%	$91.131	$91.13	$91.15	$91.10
Purchase #4	$118.50	3.746%	$122.939	$122.94	$122.95	$122.90
Purchase #5	$67.69	9.193%	$73.9127	$73.91	$73.90	$73.90
Purchase #6	$111.85	10.510%	$123.6054	$123.61	$123.60	$123.60
Purchase #7	$48.88	13.177%	$55.3209	$55.32	$55.30	$55.30
7 purchase totals =	$606.24		$657.5650	$657.57	$657.55	$657.50