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	$136.96	11.873%	$153.2213	$153.22	$153.20	$153.20
Purchase #2	$127.38	8.240%	$137.8761	$137.88	$137.90	$137.90
Purchase #3	$40.86	7.594%	$43.9629	$43.96	$43.95	$44.00
Purchase #4	$96.59	3.379%	$99.8538	$99.85	$99.85	$99.90
Purchase #5	$220.29	7.408%	$236.6091	$236.61	$236.60	$236.60
Purchase #6	$232.32	10.139%	$255.8749	$255.87	$255.85	$255.90
Purchase #7	$25.38	12.198%	$28.4759	$28.48	$28.50	$28.50
7 purchase totals =	$879.78		$955.8740	$955.87	$955.85	$956.00