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	$80.35	8.603%	$87.2625	$87.26	$87.25	$87.30
Purchase #2	$213.39	10.390%	$235.5612	$235.56	$235.55	$235.60
Purchase #3	$74.64	5.306%	$78.6004	$78.60	$78.60	$78.60
Purchase #4	$110.28	11.805%	$123.2986	$123.30	$123.30	$123.30
Purchase #5	$51.43	9.500%	$56.3159	$56.32	$56.30	$56.30
Purchase #6	$25.38	5.575%	$26.7949	$26.79	$26.80	$26.80
Purchase #7	$76.35	12.398%	$85.8159	$85.82	$85.80	$85.80
7 purchase totals =	$631.82		$693.6494	$693.65	$693.60	$693.70