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	$53.51	13.855%	$60.9238	$60.92	$60.90	$60.90
Purchase #2	$66.66	8.392%	$72.2541	$72.25	$72.25	$72.30
Purchase #3	$111.98	7.686%	$120.5868	$120.59	$120.60	$120.60
Purchase #4	$52.59	8.743%	$57.1879	$57.19	$57.20	$57.20
Purchase #5	$167.75	7.703%	$180.6718	$180.67	$180.65	$180.70
Purchase #6	$74.45	10.588%	$82.3328	$82.33	$82.35	$82.30
Purchase #7	$109.72	3.454%	$113.5097	$113.51	$113.50	$113.50
7 purchase totals =	$636.66		$687.4669	$687.46	$687.45	$687.50