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	$73.35	9.582%	$80.3784	$80.38	$80.40	$80.40
Purchase #2	$40.87	12.106%	$45.8177	$45.82	$45.80	$45.80
Purchase #3	$150.89	12.537%	$169.8071	$169.81	$169.80	$169.80
Purchase #4	$158.34	3.617%	$164.0672	$164.07	$164.05	$164.10
Purchase #5	$119.56	4.838%	$125.3443	$125.34	$125.35	$125.30
Purchase #6	$64.87	4.264%	$67.6361	$67.64	$67.65	$67.60
Purchase #7	$75.98	12.560%	$85.5231	$85.52	$85.50	$85.50
7 purchase totals =	$683.86		$738.5739	$738.58	$738.55	$738.50