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	$79.45	7.358%	$85.2959	$85.30	$85.30	$85.30
Purchase #2	$156.40	9.437%	$171.1595	$171.16	$171.15	$171.20
Purchase #3	$205.26	10.764%	$227.3542	$227.35	$227.35	$227.40
Purchase #4	$10.72	10.572%	$11.8533	$11.85	$11.85	$11.90
Purchase #5	$34.41	9.297%	$37.6091	$37.61	$37.60	$37.60
Purchase #6	$136.72	3.789%	$141.9003	$141.90	$141.90	$141.90
Purchase #7	$158.94	11.353%	$176.9845	$176.98	$177.00	$177.00
7 purchase totals =	$781.90		$852.1568	$852.15	$852.15	$852.30