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	$121.58	12.521%	$136.803	$136.80	$136.80	$136.80
Purchase #2	$93.47	11.777%	$104.478	$104.48	$104.50	$104.50
Purchase #3	$173.92	7.810%	$187.5032	$187.50	$187.50	$187.50
Purchase #4	$96.69	7.743%	$104.1767	$104.18	$104.20	$104.20
Purchase #5	$97.51	7.806%	$105.1216	$105.12	$105.10	$105.10
Purchase #6	$248.59	5.127%	$261.3352	$261.34	$261.35	$261.30
Purchase #7	$39.92	5.444%	$42.0932	$42.09	$42.10	$42.10
7 purchase totals =	$871.68		$941.5109	$941.51	$941.55	$941.50