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	$35.30	6.867%	$37.7241	$37.72	$37.70	$37.70
Purchase #2	$58.43	9.297%	$63.8622	$63.86	$63.85	$63.90
Purchase #3	$83.84	7.739%	$90.3284	$90.33	$90.35	$90.30
Purchase #4	$112.60	13.564%	$127.8731	$127.87	$127.85	$127.90
Purchase #5	$237.92	5.257%	$250.4275	$250.43	$250.45	$250.40
Purchase #6	$47.31	11.529%	$52.7644	$52.76	$52.75	$52.80
Purchase #7	$75.92	3.110%	$78.2811	$78.28	$78.30	$78.30
7 purchase totals =	$651.32		$701.2608	$701.25	$701.25	$701.30