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	$90.36	13.774%	$102.8062	$102.81	$102.80	$102.80
Purchase #2	$81.49	10.818%	$90.3056	$90.31	$90.30	$90.30
Purchase #3	$68.33	12.436%	$76.8275	$76.83	$76.85	$76.80
Purchase #4	$118.66	7.721%	$127.8217	$127.82	$127.80	$127.80
Purchase #5	$196.51	12.736%	$221.5375	$221.54	$221.55	$221.50
Purchase #6	$66.78	8.450%	$72.4229	$72.42	$72.40	$72.40
Purchase #7	$157.64	6.219%	$167.4436	$167.44	$167.45	$167.40
7 purchase totals =	$779.77		$859.1650	$859.17	$859.15	$859.00