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	$50.59	9.795%	$55.5453	$55.55	$55.55	$55.50
Purchase #2	$190.31	11.665%	$212.5097	$212.51	$212.50	$212.50
Purchase #3	$105.89	12.314%	$118.9293	$118.93	$118.95	$118.90
Purchase #4	$208.81	11.807%	$233.4642	$233.46	$233.45	$233.50
Purchase #5	$127.68	6.824%	$136.3929	$136.39	$136.40	$136.40
Purchase #6	$169.75	7.121%	$181.8379	$181.84	$181.85	$181.80
Purchase #7	$222.67	5.424%	$234.7476	$234.75	$234.75	$234.70
7 purchase totals =	$1,075.70		$1,173.4269	$1,173.43	$1,173.45	$1,173.30