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	$16.52	12.648%	$18.6094	$18.61	$18.60	$18.60
Purchase #2	$49.87	5.227%	$52.4767	$52.48	$52.50	$52.50
Purchase #3	$222.66	11.250%	$247.7093	$247.71	$247.70	$247.70
Purchase #4	$74.27	6.278%	$78.9327	$78.93	$78.95	$78.90
Purchase #5	$213.59	11.116%	$237.3327	$237.33	$237.35	$237.30
Purchase #6	$203.29	4.400%	$212.2348	$212.23	$212.25	$212.20
Purchase #7	$16.69	9.493%	$18.2744	$18.27	$18.25	$18.30
7 purchase totals =	$796.89		$865.5700	$865.56	$865.60	$865.50