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	$40.90	7.366%	$43.9127	$43.91	$43.90	$43.90
Purchase #2	$148.43	13.610%	$168.6313	$168.63	$168.65	$168.60
Purchase #3	$140.97	12.846%	$159.079	$159.08	$159.10	$159.10
Purchase #4	$138.40	10.245%	$152.5791	$152.58	$152.60	$152.60
Purchase #5	$131.32	4.185%	$136.8157	$136.82	$136.80	$136.80
Purchase #6	$54.51	7.603%	$58.6544	$58.65	$58.65	$58.70
Purchase #7	$14.29	10.789%	$15.8317	$15.83	$15.85	$15.80
7 purchase totals =	$668.82		$735.5039	$735.50	$735.55	$735.50