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	$237.48	13.822%	$270.3045	$270.30	$270.30	$270.30
Purchase #2	$173.44	3.471%	$179.4601	$179.46	$179.45	$179.50
Purchase #3	$82.37	5.448%	$86.8575	$86.86	$86.85	$86.90
Purchase #4	$184.28	4.353%	$192.3017	$192.30	$192.30	$192.30
Purchase #5	$182.35	4.152%	$189.9212	$189.92	$189.90	$189.90
Purchase #6	$34.71	8.715%	$37.735	$37.74	$37.75	$37.70
Purchase #7	$151.87	10.678%	$168.0867	$168.09	$168.10	$168.10
7 purchase totals =	$1,046.50		$1,124.6667	$1,124.67	$1,124.65	$1,124.70