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	$121.28	4.351%	$126.5569	$126.56	$126.55	$126.60
Purchase #2	$8.78	12.648%	$9.8905	$9.89	$9.90	$9.90
Purchase #3	$126.39	13.618%	$143.6018	$143.60	$143.60	$143.60
Purchase #4	$40.82	12.541%	$45.9392	$45.94	$45.95	$45.90
Purchase #5	$212.82	5.104%	$223.6823	$223.68	$223.70	$223.70
Purchase #6	$173.91	6.435%	$185.1011	$185.10	$185.10	$185.10
Purchase #7	$162.25	10.401%	$179.1256	$179.13	$179.15	$179.10
7 purchase totals =	$846.25		$913.8974	$913.90	$913.95	$913.90