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	$5.45	13.116%	$6.1648	$6.16	$6.15	$6.20
Purchase #2	$150.25	11.476%	$167.4927	$167.49	$167.50	$167.50
Purchase #3	$44.73	10.726%	$49.5277	$49.53	$49.55	$49.50
Purchase #4	$75.88	12.183%	$85.1245	$85.12	$85.10	$85.10
Purchase #5	$86.32	10.526%	$95.406	$95.41	$95.40	$95.40
Purchase #6	$201.75	8.809%	$219.5222	$219.52	$219.50	$219.50
Purchase #7	$85.80	11.765%	$95.8944	$95.89	$95.90	$95.90
7 purchase totals =	$650.18		$719.1323	$719.12	$719.10	$719.10