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	$172.83	4.129%	$179.9662	$179.97	$179.95	$180.00
Purchase #2	$86.92	3.638%	$90.0821	$90.08	$90.10	$90.10
Purchase #3	$207.90	3.517%	$215.2118	$215.21	$215.20	$215.20
Purchase #4	$136.97	4.263%	$142.809	$142.81	$142.80	$142.80
Purchase #5	$47.46	10.452%	$52.4205	$52.42	$52.40	$52.40
Purchase #6	$155.54	4.256%	$162.1598	$162.16	$162.15	$162.20
Purchase #7	$153.41	8.554%	$166.5327	$166.53	$166.55	$166.50
7 purchase totals =	$961.03		$1,009.1821	$1,009.18	$1,009.15	$1,009.20