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	$36.72	11.372%	$40.8958	$40.90	$40.90	$40.90
Purchase #2	$246.80	10.654%	$273.0941	$273.09	$273.10	$273.10
Purchase #3	$170.89	9.690%	$187.4492	$187.45	$187.45	$187.40
Purchase #4	$31.72	3.314%	$32.7712	$32.77	$32.75	$32.80
Purchase #5	$34.40	13.233%	$38.9522	$38.95	$38.95	$39.00
Purchase #6	$175.52	10.624%	$194.1672	$194.17	$194.15	$194.20
Purchase #7	$151.62	3.202%	$156.4749	$156.47	$156.45	$156.50
7 purchase totals =	$847.67		$923.8046	$923.80	$923.75	$923.90