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	$237.85	9.102%	$259.4991	$259.50	$259.50	$259.50
Purchase #2	$173.32	7.844%	$186.9152	$186.92	$186.90	$186.90
Purchase #3	$212.33	10.427%	$234.4696	$234.47	$234.45	$234.50
Purchase #4	$74.55	13.245%	$84.4241	$84.42	$84.40	$84.40
Purchase #5	$43.38	5.818%	$45.9038	$45.90	$45.90	$45.90
Purchase #6	$113.74	13.209%	$128.7639	$128.76	$128.75	$128.80
Purchase #7	$38.25	13.812%	$43.5331	$43.53	$43.55	$43.50
7 purchase totals =	$893.42		$983.5088	$983.50	$983.45	$983.50