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	$77.28	8.861%	$84.1278	$84.13	$84.15	$84.10
Purchase #2	$56.26	6.375%	$59.8466	$59.85	$59.85	$59.80
Purchase #3	$243.98	4.628%	$255.2714	$255.27	$255.25	$255.30
Purchase #4	$46.79	12.182%	$52.49	$52.49	$52.50	$52.50
Purchase #5	$93.87	4.756%	$98.3345	$98.33	$98.35	$98.30
Purchase #6	$10.26	6.214%	$10.8976	$10.90	$10.90	$10.90
Purchase #7	$18.49	11.103%	$20.5429	$20.54	$20.55	$20.50
7 purchase totals =	$546.93		$581.5108	$581.51	$581.55	$581.40