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	$110.26	11.819%	$123.2916	$123.29	$123.30	$123.30
Purchase #2	$218.88	8.520%	$237.5286	$237.53	$237.55	$237.50
Purchase #3	$40.98	4.448%	$42.8028	$42.80	$42.80	$42.80
Purchase #4	$154.31	11.670%	$172.318	$172.32	$172.30	$172.30
Purchase #5	$110.81	5.519%	$116.9256	$116.93	$116.95	$116.90
Purchase #6	$168.42	5.772%	$178.1412	$178.14	$178.15	$178.10
Purchase #7	$88.60	3.334%	$91.5539	$91.55	$91.55	$91.60
7 purchase totals =	$892.26		$962.5617	$962.56	$962.60	$962.50