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	$223.55	3.517%	$231.4123	$231.41	$231.40	$231.40
Purchase #2	$75.25	8.729%	$81.8186	$81.82	$81.80	$81.80
Purchase #3	$70.83	6.547%	$75.4672	$75.47	$75.45	$75.50
Purchase #4	$220.78	6.446%	$235.0115	$235.01	$235.00	$235.00
Purchase #5	$200.38	7.243%	$214.8935	$214.89	$214.90	$214.90
Purchase #6	$69.66	13.267%	$78.9018	$78.90	$78.90	$78.90
Purchase #7	$233.33	13.397%	$264.5892	$264.59	$264.60	$264.60
7 purchase totals =	$1,093.78		$1,182.0941	$1,182.09	$1,182.05	$1,182.10