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	$139.91	13.807%	$159.2274	$159.23	$159.25	$159.20
Purchase #2	$164.34	3.388%	$169.9078	$169.91	$169.90	$169.90
Purchase #3	$117.55	7.680%	$126.5778	$126.58	$126.60	$126.60
Purchase #4	$169.51	5.113%	$178.177	$178.18	$178.20	$178.20
Purchase #5	$68.63	13.469%	$77.8738	$77.87	$77.85	$77.90
Purchase #6	$239.72	6.486%	$255.2682	$255.27	$255.25	$255.30
Purchase #7	$204.59	4.175%	$213.1316	$213.13	$213.15	$213.10
7 purchase totals =	$1,104.25		$1,180.1636	$1,180.17	$1,180.20	$1,180.20