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	$212.93	12.279%	$239.0757	$239.08	$239.10	$239.10
Purchase #2	$106.28	10.187%	$117.1067	$117.11	$117.10	$117.10
Purchase #3	$92.71	7.582%	$99.7393	$99.74	$99.75	$99.70
Purchase #4	$86.39	4.491%	$90.2698	$90.27	$90.25	$90.30
Purchase #5	$156.29	5.462%	$164.8266	$164.83	$164.85	$164.80
Purchase #6	$224.95	10.824%	$249.2986	$249.30	$249.30	$249.30
Purchase #7	$132.59	7.557%	$142.6098	$142.61	$142.60	$142.60
7 purchase totals =	$1,012.14		$1,102.9265	$1,102.94	$1,102.95	$1,102.90