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	$39.60	6.759%	$42.2766	$42.28	$42.30	$42.30
Purchase #2	$171.59	8.336%	$185.8937	$185.89	$185.90	$185.90
Purchase #3	$92.52	9.649%	$101.4473	$101.45	$101.45	$101.40
Purchase #4	$219.76	5.113%	$230.9963	$231.00	$231.00	$231.00
Purchase #5	$47.69	4.624%	$49.8952	$49.90	$49.90	$49.90
Purchase #6	$107.73	12.401%	$121.0896	$121.09	$121.10	$121.10
Purchase #7	$131.50	13.205%	$148.8646	$148.86	$148.85	$148.90
7 purchase totals =	$810.39		$880.4633	$880.47	$880.50	$880.50