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	$240.79	13.444%	$273.1618	$273.16	$273.15	$273.20
Purchase #2	$96.31	12.761%	$108.6001	$108.60	$108.60	$108.60
Purchase #3	$172.75	10.553%	$190.9803	$190.98	$191.00	$191.00
Purchase #4	$13.86	4.420%	$14.4726	$14.47	$14.45	$14.50
Purchase #5	$171.68	7.473%	$184.5096	$184.51	$184.50	$184.50
Purchase #6	$223.32	13.647%	$253.7965	$253.80	$253.80	$253.80
Purchase #7	$208.53	3.804%	$216.4625	$216.46	$216.45	$216.50
7 purchase totals =	$1,127.24		$1,241.9834	$1,241.98	$1,241.95	$1,242.10