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	$31.61	3.781%	$32.8052	$32.81	$32.80	$32.80
Purchase #2	$144.81	13.390%	$164.2001	$164.20	$164.20	$164.20
Purchase #3	$240.31	10.479%	$265.4921	$265.49	$265.50	$265.50
Purchase #4	$74.84	7.552%	$80.4919	$80.49	$80.50	$80.50
Purchase #5	$53.51	7.156%	$57.3392	$57.34	$57.35	$57.30
Purchase #6	$26.71	8.333%	$28.9357	$28.94	$28.95	$28.90
Purchase #7	$186.74	5.137%	$196.3328	$196.33	$196.35	$196.30
7 purchase totals =	$758.53		$825.5970	$825.60	$825.65	$825.50