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	$142.66	6.194%	$151.4964	$151.50	$151.50	$151.50
Purchase #2	$45.86	7.854%	$49.4618	$49.46	$49.45	$49.50
Purchase #3	$225.49	12.145%	$252.8758	$252.88	$252.90	$252.90
Purchase #4	$31.57	4.773%	$33.0768	$33.08	$33.10	$33.10
Purchase #5	$85.83	4.640%	$89.8125	$89.81	$89.80	$89.80
Purchase #6	$41.95	13.705%	$47.6992	$47.70	$47.70	$47.70
Purchase #7	$39.88	5.262%	$41.9785	$41.98	$42.00	$42.00
7 purchase totals =	$613.24		$666.4010	$666.41	$666.45	$666.50