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	$146.90	8.859%	$159.9139	$159.91	$159.90	$159.90
Purchase #2	$60.50	11.198%	$67.2748	$67.27	$67.25	$67.30
Purchase #3	$218.52	10.469%	$241.3969	$241.40	$241.40	$241.40
Purchase #4	$30.31	11.852%	$33.9023	$33.90	$33.90	$33.90
Purchase #5	$85.73	7.345%	$92.0269	$92.03	$92.05	$92.00
Purchase #6	$163.96	4.605%	$171.5104	$171.51	$171.50	$171.50
Purchase #7	$162.60	10.308%	$179.3608	$179.36	$179.35	$179.40
7 purchase totals =	$868.52		$945.3860	$945.38	$945.35	$945.40