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	$112.95	13.252%	$127.9181	$127.92	$127.90	$127.90
Purchase #2	$102.79	5.833%	$108.7857	$108.79	$108.80	$108.80
Purchase #3	$50.69	9.641%	$55.577	$55.58	$55.60	$55.60
Purchase #4	$86.65	7.116%	$92.816	$92.82	$92.80	$92.80
Purchase #5	$33.92	3.587%	$35.1367	$35.14	$35.15	$35.10
Purchase #6	$174.30	6.412%	$185.4761	$185.48	$185.50	$185.50
Purchase #7	$210.67	7.251%	$225.9457	$225.95	$225.95	$225.90
7 purchase totals =	$771.97		$831.6553	$831.68	$831.70	$831.60