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	$45.55	11.813%	$50.9308	$50.93	$50.95	$50.90
Purchase #2	$192.28	10.579%	$212.6213	$212.62	$212.60	$212.60
Purchase #3	$158.72	8.742%	$172.5953	$172.60	$172.60	$172.60
Purchase #4	$210.78	5.710%	$222.8155	$222.82	$222.80	$222.80
Purchase #5	$239.71	11.199%	$266.5551	$266.56	$266.55	$266.60
Purchase #6	$182.32	10.401%	$201.2831	$201.28	$201.30	$201.30
Purchase #7	$35.31	13.664%	$40.1348	$40.13	$40.15	$40.10
7 purchase totals =	$1,064.67		$1,166.9359	$1,166.94	$1,166.95	$1,166.90