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	$203.50	9.299%	$222.4235	$222.42	$222.40	$222.40
Purchase #2	$144.62	4.164%	$150.642	$150.64	$150.65	$150.60
Purchase #3	$125.61	7.344%	$134.8348	$134.83	$134.85	$134.80
Purchase #4	$193.88	9.465%	$212.2307	$212.23	$212.25	$212.20
Purchase #5	$91.68	9.671%	$100.5464	$100.55	$100.55	$100.50
Purchase #6	$36.42	6.779%	$38.8889	$38.89	$38.90	$38.90
Purchase #7	$47.32	3.400%	$48.9289	$48.93	$48.95	$48.90
7 purchase totals =	$843.03		$908.4952	$908.49	$908.55	$908.30