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	$71.49	10.255%	$78.8213	$78.82	$78.80	$78.80
Purchase #2	$41.37	5.316%	$43.5692	$43.57	$43.55	$43.60
Purchase #3	$109.54	13.138%	$123.9314	$123.93	$123.95	$123.90
Purchase #4	$200.35	5.742%	$211.8541	$211.85	$211.85	$211.90
Purchase #5	$71.58	10.116%	$78.821	$78.82	$78.80	$78.80
Purchase #6	$208.43	13.396%	$236.3513	$236.35	$236.35	$236.40
Purchase #7	$81.76	13.262%	$92.603	$92.60	$92.60	$92.60
7 purchase totals =	$784.52		$865.9513	$865.94	$865.90	$866.00