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	$139.56	11.295%	$155.3233	$155.32	$155.30	$155.30
Purchase #2	$161.68	11.695%	$180.5885	$180.59	$180.60	$180.60
Purchase #3	$127.60	9.658%	$139.9236	$139.92	$139.90	$139.90
Purchase #4	$236.33	10.209%	$260.4569	$260.46	$260.45	$260.50
Purchase #5	$70.28	12.143%	$78.8141	$78.81	$78.80	$78.80
Purchase #6	$119.76	6.539%	$127.5911	$127.59	$127.60	$127.60
Purchase #7	$88.28	8.255%	$95.5675	$95.57	$95.55	$95.60
7 purchase totals =	$943.49		$1,038.2650	$1,038.26	$1,038.20	$1,038.30