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	$176.80	5.509%	$186.5399	$186.54	$186.55	$186.50
Purchase #2	$51.94	3.265%	$53.6358	$53.64	$53.65	$53.60
Purchase #3	$210.73	3.463%	$218.0276	$218.03	$218.05	$218.00
Purchase #4	$139.93	12.470%	$157.3793	$157.38	$157.40	$157.40
Purchase #5	$111.45	6.172%	$118.3287	$118.33	$118.35	$118.30
Purchase #6	$43.44	3.672%	$45.0351	$45.04	$45.05	$45.00
Purchase #7	$146.37	12.284%	$164.3501	$164.35	$164.35	$164.40
7 purchase totals =	$880.66		$943.2965	$943.31	$943.40	$943.20