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	$105.73	6.425%	$112.5232	$112.52	$112.50	$112.50
Purchase #2	$71.79	11.725%	$80.2074	$80.21	$80.20	$80.20
Purchase #3	$23.34	8.620%	$25.3519	$25.35	$25.35	$25.40
Purchase #4	$178.75	6.451%	$190.2812	$190.28	$190.30	$190.30
Purchase #5	$126.73	3.848%	$131.6066	$131.61	$131.60	$131.60
Purchase #6	$81.46	9.828%	$89.4659	$89.47	$89.45	$89.50
Purchase #7	$6.28	13.475%	$7.1262	$7.13	$7.15	$7.10
7 purchase totals =	$594.08		$636.5624	$636.57	$636.55	$636.60