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	$29.98	3.600%	$31.0593	$31.06	$31.05	$31.10
Purchase #2	$62.89	11.851%	$70.3431	$70.34	$70.35	$70.30
Purchase #3	$80.67	7.665%	$86.8534	$86.85	$86.85	$86.90
Purchase #4	$212.62	4.637%	$222.4792	$222.48	$222.50	$222.50
Purchase #5	$224.71	5.768%	$237.6713	$237.67	$237.65	$237.70
Purchase #6	$80.39	12.800%	$90.6799	$90.68	$90.70	$90.70
Purchase #7	$175.41	8.346%	$190.0497	$190.05	$190.05	$190.00
7 purchase totals =	$866.67		$929.1359	$929.13	$929.15	$929.20