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	$78.90	8.709%	$85.7714	$85.77	$85.75	$85.80
Purchase #2	$61.67	10.738%	$68.2921	$68.29	$68.30	$68.30
Purchase #3	$123.75	7.111%	$132.5499	$132.55	$132.55	$132.50
Purchase #4	$9.32	11.530%	$10.3946	$10.39	$10.40	$10.40
Purchase #5	$83.76	10.272%	$92.3638	$92.36	$92.35	$92.40
Purchase #6	$112.99	12.665%	$127.3002	$127.30	$127.30	$127.30
Purchase #7	$145.98	3.279%	$150.7667	$150.77	$150.75	$150.80
7 purchase totals =	$616.37		$667.4387	$667.43	$667.40	$667.50