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	$78.37	9.750%	$86.0111	$86.01	$86.00	$86.00
Purchase #2	$60.97	5.270%	$64.1831	$64.18	$64.20	$64.20
Purchase #3	$31.54	6.544%	$33.604	$33.60	$33.60	$33.60
Purchase #4	$62.84	6.251%	$66.7681	$66.77	$66.75	$66.80
Purchase #5	$58.67	11.143%	$65.2076	$65.21	$65.20	$65.20
Purchase #6	$118.78	11.492%	$132.4302	$132.43	$132.45	$132.40
Purchase #7	$56.59	4.654%	$59.2237	$59.22	$59.20	$59.20
7 purchase totals =	$467.76		$507.4278	$507.42	$507.40	$507.40