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	$86.42	9.669%	$94.7759	$94.78	$94.80	$94.80
Purchase #2	$222.25	10.279%	$245.0951	$245.10	$245.10	$245.10
Purchase #3	$118.66	3.541%	$122.8618	$122.86	$122.85	$122.90
Purchase #4	$177.35	7.114%	$189.9667	$189.97	$189.95	$190.00
Purchase #5	$74.79	4.861%	$78.4255	$78.43	$78.45	$78.40
Purchase #6	$75.26	4.427%	$78.5918	$78.59	$78.60	$78.60
Purchase #7	$79.42	13.611%	$90.2299	$90.23	$90.25	$90.20
7 purchase totals =	$834.15		$899.9467	$899.96	$900.00	$900.00