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	$145.56	13.151%	$164.7026	$164.70	$164.70	$164.70
Purchase #2	$179.51	3.237%	$185.3207	$185.32	$185.30	$185.30
Purchase #3	$156.28	10.704%	$173.0082	$173.01	$173.00	$173.00
Purchase #4	$72.51	9.405%	$79.3296	$79.33	$79.35	$79.30
Purchase #5	$134.61	4.632%	$140.8451	$140.85	$140.85	$140.80
Purchase #6	$159.96	7.658%	$172.2097	$172.21	$172.20	$172.20
Purchase #7	$6.86	8.322%	$7.4309	$7.43	$7.45	$7.40
7 purchase totals =	$855.29		$922.8468	$922.85	$922.85	$922.70