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	$130.82	9.741%	$143.5632	$143.56	$143.55	$143.60
Purchase #2	$32.40	10.649%	$35.8503	$35.85	$35.85	$35.90
Purchase #3	$200.86	13.588%	$228.1529	$228.15	$228.15	$228.20
Purchase #4	$19.45	7.550%	$20.9185	$20.92	$20.90	$20.90
Purchase #5	$32.60	9.184%	$35.594	$35.59	$35.60	$35.60
Purchase #6	$212.98	11.292%	$237.0297	$237.03	$237.05	$237.00
Purchase #7	$159.92	12.583%	$180.0427	$180.04	$180.05	$180.00
7 purchase totals =	$789.03		$881.1513	$881.14	$881.15	$881.20