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	$18.66	7.573%	$20.0731	$20.07	$20.05	$20.10
Purchase #2	$30.26	3.855%	$31.4265	$31.43	$31.45	$31.40
Purchase #3	$237.90	10.698%	$263.3505	$263.35	$263.35	$263.40
Purchase #4	$67.36	4.680%	$70.5124	$70.51	$70.50	$70.50
Purchase #5	$177.56	3.712%	$184.151	$184.15	$184.15	$184.20
Purchase #6	$68.80	5.336%	$72.4712	$72.47	$72.45	$72.50
Purchase #7	$220.42	12.127%	$247.1503	$247.15	$247.15	$247.20
7 purchase totals =	$820.96		$889.1350	$889.13	$889.10	$889.30