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	$229.53	11.784%	$256.5778	$256.58	$256.60	$256.60
Purchase #2	$163.85	8.833%	$178.3229	$178.32	$178.30	$178.30
Purchase #3	$65.27	11.465%	$72.7532	$72.75	$72.75	$72.80
Purchase #4	$236.85	10.183%	$260.9684	$260.97	$260.95	$261.00
Purchase #5	$146.91	4.486%	$153.5004	$153.50	$153.50	$153.50
Purchase #6	$87.38	3.541%	$90.4741	$90.47	$90.45	$90.50
Purchase #7	$83.60	5.625%	$88.3025	$88.30	$88.30	$88.30
7 purchase totals =	$1,013.39		$1,100.8993	$1,100.89	$1,100.85	$1,101.00