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	$118.69	10.871%	$131.5928	$131.59	$131.60	$131.60
Purchase #2	$116.62	4.178%	$121.4924	$121.49	$121.50	$121.50
Purchase #3	$42.95	10.409%	$47.4207	$47.42	$47.40	$47.40
Purchase #4	$19.68	6.365%	$20.9326	$20.93	$20.95	$20.90
Purchase #5	$147.50	12.419%	$165.818	$165.82	$165.80	$165.80
Purchase #6	$69.39	7.542%	$74.6234	$74.62	$74.60	$74.60
Purchase #7	$72.29	11.483%	$80.5911	$80.59	$80.60	$80.60
7 purchase totals =	$587.12		$642.4710	$642.46	$642.45	$642.40