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	$85.42	5.873%	$90.4367	$90.44	$90.45	$90.40
Purchase #2	$44.53	6.494%	$47.4218	$47.42	$47.40	$47.40
Purchase #3	$5.93	12.403%	$6.6655	$6.67	$6.65	$6.70
Purchase #4	$81.57	10.307%	$89.9774	$89.98	$90.00	$90.00
Purchase #5	$220.56	7.576%	$237.2696	$237.27	$237.25	$237.30
Purchase #6	$249.58	9.762%	$273.944	$273.94	$273.95	$273.90
Purchase #7	$34.78	3.133%	$35.8697	$35.87	$35.85	$35.90
7 purchase totals =	$722.37		$781.5847	$781.59	$781.55	$781.60