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	$132.43	7.601%	$142.496	$142.50	$142.50	$142.50
Purchase #2	$103.73	12.649%	$116.8508	$116.85	$116.85	$116.90
Purchase #3	$208.77	9.708%	$229.0374	$229.04	$229.05	$229.00
Purchase #4	$86.43	5.216%	$90.9382	$90.94	$90.95	$90.90
Purchase #5	$238.89	7.177%	$256.0351	$256.04	$256.05	$256.00
Purchase #6	$8.51	5.279%	$8.9592	$8.96	$8.95	$9.00
Purchase #7	$58.70	5.469%	$61.9103	$61.91	$61.90	$61.90
7 purchase totals =	$837.46		$906.2270	$906.24	$906.25	$906.20