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	$138.45	4.370%	$144.5003	$144.50	$144.50	$144.50
Purchase #2	$155.84	5.444%	$164.3239	$164.32	$164.30	$164.30
Purchase #3	$31.39	11.197%	$34.9047	$34.90	$34.90	$34.90
Purchase #4	$35.46	7.223%	$38.0213	$38.02	$38.00	$38.00
Purchase #5	$151.89	8.282%	$164.4695	$164.47	$164.45	$164.50
Purchase #6	$89.33	4.103%	$92.9952	$93.00	$93.00	$93.00
Purchase #7	$237.86	11.195%	$264.4884	$264.49	$264.50	$264.50
7 purchase totals =	$840.22		$903.7033	$903.70	$903.65	$903.70