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	$150.37	9.649%	$164.8792	$164.88	$164.90	$164.90
Purchase #2	$69.69	12.774%	$78.5922	$78.59	$78.60	$78.60
Purchase #3	$67.67	7.573%	$72.7946	$72.79	$72.80	$72.80
Purchase #4	$87.94	3.240%	$90.7893	$90.79	$90.80	$90.80
Purchase #5	$65.91	7.623%	$70.9343	$70.93	$70.95	$70.90
Purchase #6	$27.50	7.423%	$29.5413	$29.54	$29.55	$29.50
Purchase #7	$64.92	12.325%	$72.9214	$72.92	$72.90	$72.90
7 purchase totals =	$534.00		$580.4523	$580.44	$580.50	$580.40