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	$101.32	9.709%	$111.1572	$111.16	$111.15	$111.20
Purchase #2	$233.80	9.869%	$256.8737	$256.87	$256.85	$256.90
Purchase #3	$41.27	13.830%	$46.9776	$46.98	$47.00	$47.00
Purchase #4	$166.86	5.624%	$176.2442	$176.24	$176.25	$176.20
Purchase #5	$135.69	6.772%	$144.8789	$144.88	$144.90	$144.90
Purchase #6	$58.25	12.187%	$65.3489	$65.35	$65.35	$65.30
Purchase #7	$112.86	11.538%	$125.8818	$125.88	$125.90	$125.90
7 purchase totals =	$850.05		$927.3623	$927.36	$927.40	$927.40