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	$37.43	7.746%	$40.3293	$40.33	$40.35	$40.30
Purchase #2	$87.39	11.445%	$97.3918	$97.39	$97.40	$97.40
Purchase #3	$165.67	12.463%	$186.3175	$186.32	$186.30	$186.30
Purchase #4	$146.52	8.377%	$158.794	$158.79	$158.80	$158.80
Purchase #5	$66.84	5.497%	$70.5142	$70.51	$70.50	$70.50
Purchase #6	$224.46	8.401%	$243.3169	$243.32	$243.30	$243.30
Purchase #7	$81.91	8.578%	$88.9362	$88.94	$88.95	$88.90
7 purchase totals =	$810.22		$885.5999	$885.60	$885.60	$885.50