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	$30.35	13.186%	$34.352	$34.35	$34.35	$34.40
Purchase #2	$38.88	12.525%	$43.7497	$43.75	$43.75	$43.70
Purchase #3	$92.43	7.801%	$99.6405	$99.64	$99.65	$99.60
Purchase #4	$12.66	12.679%	$14.2652	$14.27	$14.25	$14.30
Purchase #5	$42.47	5.172%	$44.6665	$44.67	$44.65	$44.70
Purchase #6	$162.25	6.160%	$172.2446	$172.24	$172.25	$172.20
Purchase #7	$250.43	5.155%	$263.3397	$263.34	$263.35	$263.30
7 purchase totals =	$629.47		$672.2582	$672.26	$672.25	$672.20