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	$55.61	7.154%	$59.5883	$59.59	$59.60	$59.60
Purchase #2	$57.88	8.696%	$62.9132	$62.91	$62.90	$62.90
Purchase #3	$84.74	6.337%	$90.11	$90.11	$90.10	$90.10
Purchase #4	$152.63	13.552%	$173.3144	$173.31	$173.30	$173.30
Purchase #5	$151.75	10.726%	$168.0267	$168.03	$168.05	$168.00
Purchase #6	$105.34	6.150%	$111.8184	$111.82	$111.80	$111.80
Purchase #7	$47.94	3.230%	$49.4885	$49.49	$49.50	$49.50
7 purchase totals =	$655.89		$715.2595	$715.26	$715.25	$715.20