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	$102.46	9.804%	$112.5052	$112.51	$112.50	$112.50
Purchase #2	$108.37	11.800%	$121.1577	$121.16	$121.15	$121.20
Purchase #3	$71.33	13.799%	$81.1728	$81.17	$81.15	$81.20
Purchase #4	$250.65	13.735%	$285.0768	$285.08	$285.10	$285.10
Purchase #5	$7.40	7.341%	$7.9432	$7.94	$7.95	$7.90
Purchase #6	$90.82	11.639%	$101.3905	$101.39	$101.40	$101.40
Purchase #7	$48.57	11.684%	$54.2449	$54.24	$54.25	$54.20
7 purchase totals =	$679.60		$763.4911	$763.49	$763.50	$763.50