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	$225.89	6.298%	$240.1166	$240.12	$240.10	$240.10
Purchase #2	$59.68	12.114%	$66.9096	$66.91	$66.90	$66.90
Purchase #3	$34.84	11.633%	$38.8929	$38.89	$38.90	$38.90
Purchase #4	$31.74	3.302%	$32.7881	$32.79	$32.80	$32.80
Purchase #5	$63.25	13.176%	$71.5838	$71.58	$71.60	$71.60
Purchase #6	$56.96	8.646%	$61.8848	$61.88	$61.90	$61.90
Purchase #7	$39.56	13.154%	$44.7637	$44.76	$44.75	$44.80
7 purchase totals =	$511.92		$556.9395	$556.93	$556.95	$557.00