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	$141.89	10.368%	$156.6012	$156.60	$156.60	$156.60
Purchase #2	$59.71	11.436%	$66.5384	$66.54	$66.55	$66.50
Purchase #3	$187.30	11.281%	$208.4293	$208.43	$208.45	$208.40
Purchase #4	$249.44	8.537%	$270.7347	$270.73	$270.75	$270.70
Purchase #5	$53.59	11.198%	$59.591	$59.59	$59.60	$59.60
Purchase #6	$165.66	9.730%	$181.7787	$181.78	$181.80	$181.80
Purchase #7	$33.49	4.150%	$34.8798	$34.88	$34.90	$34.90
7 purchase totals =	$891.08		$978.5531	$978.55	$978.65	$978.50