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	$8.61	12.870%	$9.7181	$9.72	$9.70	$9.70
Purchase #2	$29.43	5.383%	$31.0142	$31.01	$31.00	$31.00
Purchase #3	$103.75	7.360%	$111.386	$111.39	$111.40	$111.40
Purchase #4	$169.65	11.273%	$188.7746	$188.77	$188.75	$188.80
Purchase #5	$190.39	9.693%	$208.8445	$208.84	$208.85	$208.80
Purchase #6	$72.42	13.443%	$82.1554	$82.16	$82.15	$82.20
Purchase #7	$84.69	13.387%	$96.0275	$96.03	$96.05	$96.00
7 purchase totals =	$658.94		$727.9203	$727.92	$727.90	$727.90