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	$45.49	7.249%	$48.7876	$48.79	$48.80	$48.80
Purchase #2	$219.66	10.438%	$242.5881	$242.59	$242.60	$242.60
Purchase #3	$177.44	9.250%	$193.8532	$193.85	$193.85	$193.90
Purchase #4	$44.78	12.704%	$50.4689	$50.47	$50.45	$50.50
Purchase #5	$66.50	7.250%	$71.3213	$71.32	$71.30	$71.30
Purchase #6	$78.31	7.129%	$83.8927	$83.89	$83.90	$83.90
Purchase #7	$100.42	9.299%	$109.7581	$109.76	$109.75	$109.80
7 purchase totals =	$732.60		$800.6699	$800.67	$800.65	$800.80