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	$180.33	3.403%	$186.4666	$186.47	$186.45	$186.50
Purchase #2	$192.68	10.806%	$213.501	$213.50	$213.50	$213.50
Purchase #3	$133.84	6.327%	$142.3081	$142.31	$142.30	$142.30
Purchase #4	$137.59	11.820%	$153.8531	$153.85	$153.85	$153.90
Purchase #5	$164.86	5.126%	$173.3107	$173.31	$173.30	$173.30
Purchase #6	$17.56	10.810%	$19.4582	$19.46	$19.45	$19.50
Purchase #7	$94.88	7.571%	$102.0634	$102.06	$102.05	$102.10
7 purchase totals =	$921.74		$990.9611	$990.96	$990.90	$991.10