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	$117.99	8.257%	$127.7324	$127.73	$127.75	$127.70
Purchase #2	$137.74	3.710%	$142.8502	$142.85	$142.85	$142.90
Purchase #3	$48.65	11.256%	$54.126	$54.13	$54.15	$54.10
Purchase #4	$111.54	4.307%	$116.344	$116.34	$116.35	$116.30
Purchase #5	$158.82	5.497%	$167.5503	$167.55	$167.55	$167.60
Purchase #6	$129.88	13.868%	$147.8918	$147.89	$147.90	$147.90
Purchase #7	$229.88	3.227%	$237.2982	$237.30	$237.30	$237.30
7 purchase totals =	$934.50		$993.7929	$993.79	$993.85	$993.80