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	$6.87	3.306%	$7.0971	$7.10	$7.10	$7.10
Purchase #2	$81.46	11.566%	$90.8817	$90.88	$90.90	$90.90
Purchase #3	$106.96	12.177%	$119.9845	$119.98	$120.00	$120.00
Purchase #4	$46.78	12.821%	$52.7777	$52.78	$52.80	$52.80
Purchase #5	$133.59	12.461%	$150.2366	$150.24	$150.25	$150.20
Purchase #6	$36.59	8.708%	$39.7763	$39.78	$39.80	$39.80
Purchase #7	$109.75	7.771%	$118.2787	$118.28	$118.30	$118.30
7 purchase totals =	$522.00		$579.0326	$579.04	$579.15	$579.10