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	$136.55	6.303%	$145.1567	$145.16	$145.15	$145.20
Purchase #2	$22.79	12.437%	$25.6244	$25.62	$25.60	$25.60
Purchase #3	$51.50	13.772%	$58.5926	$58.59	$58.60	$58.60
Purchase #4	$159.90	10.591%	$176.835	$176.84	$176.85	$176.80
Purchase #5	$56.35	13.372%	$63.8851	$63.89	$63.90	$63.90
Purchase #6	$62.42	7.713%	$67.2345	$67.23	$67.25	$67.20
Purchase #7	$97.68	13.856%	$111.2145	$111.21	$111.20	$111.20
7 purchase totals =	$587.19		$648.5428	$648.54	$648.55	$648.50