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	$131.90	11.713%	$147.3494	$147.35	$147.35	$147.30
Purchase #2	$138.92	8.391%	$150.5768	$150.58	$150.60	$150.60
Purchase #3	$166.57	11.509%	$185.7405	$185.74	$185.75	$185.70
Purchase #4	$164.91	5.454%	$173.9042	$173.90	$173.90	$173.90
Purchase #5	$120.67	7.740%	$130.0099	$130.01	$130.00	$130.00
Purchase #6	$250.90	11.329%	$279.3245	$279.32	$279.30	$279.30
Purchase #7	$103.93	10.123%	$114.4508	$114.45	$114.45	$114.50
7 purchase totals =	$1,077.80		$1,181.3561	$1,181.35	$1,181.35	$1,181.30