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	$57.50	10.383%	$63.4702	$63.47	$63.45	$63.50
Purchase #2	$132.57	11.251%	$147.4855	$147.49	$147.50	$147.50
Purchase #3	$29.29	6.517%	$31.1988	$31.20	$31.20	$31.20
Purchase #4	$231.79	3.775%	$240.5401	$240.54	$240.55	$240.50
Purchase #5	$111.32	10.712%	$123.2446	$123.24	$123.25	$123.20
Purchase #6	$5.66	12.506%	$6.3678	$6.37	$6.35	$6.40
Purchase #7	$55.30	8.233%	$59.8528	$59.85	$59.85	$59.90
7 purchase totals =	$623.43		$672.1598	$672.16	$672.15	$672.20