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	$218.79	13.613%	$248.5739	$248.57	$248.55	$248.60
Purchase #2	$53.49	3.712%	$55.4755	$55.48	$55.50	$55.50
Purchase #3	$68.48	7.227%	$73.429	$73.43	$73.45	$73.40
Purchase #4	$33.32	13.347%	$37.7672	$37.77	$37.75	$37.80
Purchase #5	$86.50	4.731%	$90.5923	$90.59	$90.60	$90.60
Purchase #6	$55.75	7.577%	$59.9742	$59.97	$59.95	$60.00
Purchase #7	$27.48	13.811%	$31.2753	$31.28	$31.30	$31.30
7 purchase totals =	$543.81		$597.0874	$597.09	$597.10	$597.20