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	$56.60	5.129%	$59.503	$59.50	$59.50	$59.50
Purchase #2	$163.55	6.284%	$173.8275	$173.83	$173.85	$173.80
Purchase #3	$153.93	9.677%	$168.8258	$168.83	$168.85	$168.80
Purchase #4	$211.53	8.482%	$229.472	$229.47	$229.45	$229.50
Purchase #5	$121.34	7.315%	$130.216	$130.22	$130.20	$130.20
Purchase #6	$5.82	10.620%	$6.4381	$6.44	$6.45	$6.40
Purchase #7	$133.58	10.111%	$147.0863	$147.09	$147.10	$147.10
7 purchase totals =	$846.35		$915.3687	$915.38	$915.40	$915.30