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	$210.94	13.464%	$239.341	$239.34	$239.35	$239.30
Purchase #2	$142.36	10.160%	$156.8238	$156.82	$156.80	$156.80
Purchase #3	$182.59	13.315%	$206.9019	$206.90	$206.90	$206.90
Purchase #4	$247.63	3.163%	$255.4625	$255.46	$255.45	$255.50
Purchase #5	$83.93	6.752%	$89.597	$89.60	$89.60	$89.60
Purchase #6	$47.46	9.443%	$51.9416	$51.94	$51.95	$51.90
Purchase #7	$100.32	9.519%	$109.8695	$109.87	$109.85	$109.90
7 purchase totals =	$1,015.23		$1,109.9373	$1,109.93	$1,109.90	$1,109.90