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	$142.37	11.682%	$159.0017	$159.00	$159.00	$159.00
Purchase #2	$170.45	6.541%	$181.5991	$181.60	$181.60	$181.60
Purchase #3	$156.27	10.528%	$172.7221	$172.72	$172.70	$172.70
Purchase #4	$159.55	8.526%	$173.1532	$173.15	$173.15	$173.20
Purchase #5	$75.68	10.805%	$83.8572	$83.86	$83.85	$83.90
Purchase #6	$6.76	11.303%	$7.5241	$7.52	$7.50	$7.50
Purchase #7	$90.47	6.238%	$96.1135	$96.11	$96.10	$96.10
7 purchase totals =	$801.55		$873.9709	$873.96	$873.90	$874.00