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	$41.50	4.814%	$43.4978	$43.50	$43.50	$43.50
Purchase #2	$198.63	8.431%	$215.3765	$215.38	$215.40	$215.40
Purchase #3	$87.68	9.354%	$95.8816	$95.88	$95.90	$95.90
Purchase #4	$222.79	11.117%	$247.5576	$247.56	$247.55	$247.60
Purchase #5	$26.90	10.159%	$29.6328	$29.63	$29.65	$29.60
Purchase #6	$100.89	8.680%	$109.6473	$109.65	$109.65	$109.60
Purchase #7	$41.73	9.579%	$45.7273	$45.73	$45.75	$45.70
7 purchase totals =	$720.12		$787.3209	$787.33	$787.40	$787.30