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	$45.95	13.147%	$51.991	$51.99	$52.00	$52.00
Purchase #2	$83.76	10.545%	$92.5925	$92.59	$92.60	$92.60
Purchase #3	$80.48	5.675%	$85.0472	$85.05	$85.05	$85.00
Purchase #4	$21.82	12.786%	$24.6099	$24.61	$24.60	$24.60
Purchase #5	$27.46	6.792%	$29.3251	$29.33	$29.35	$29.30
Purchase #6	$250.58	11.432%	$279.2263	$279.23	$279.25	$279.20
Purchase #7	$101.79	3.239%	$105.087	$105.09	$105.10	$105.10
7 purchase totals =	$611.84		$667.8790	$667.89	$667.95	$667.80