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	$144.38	12.769%	$162.8159	$162.82	$162.80	$162.80
Purchase #2	$233.25	13.859%	$265.5761	$265.58	$265.60	$265.60
Purchase #3	$126.59	4.123%	$131.8093	$131.81	$131.80	$131.80
Purchase #4	$68.43	9.784%	$75.1252	$75.13	$75.15	$75.10
Purchase #5	$94.95	3.656%	$98.4214	$98.42	$98.40	$98.40
Purchase #6	$131.28	7.848%	$141.5829	$141.58	$141.60	$141.60
Purchase #7	$202.37	5.690%	$213.8849	$213.88	$213.90	$213.90
7 purchase totals =	$1,001.25		$1,089.2157	$1,089.22	$1,089.25	$1,089.20