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	$44.59	8.548%	$48.4016	$48.40	$48.40	$48.40
Purchase #2	$181.86	4.226%	$189.5454	$189.55	$189.55	$189.50
Purchase #3	$75.48	4.538%	$78.9053	$78.91	$78.90	$78.90
Purchase #4	$249.96	8.865%	$272.119	$272.12	$272.10	$272.10
Purchase #5	$208.30	8.161%	$225.2994	$225.30	$225.30	$225.30
Purchase #6	$48.82	4.658%	$51.094	$51.09	$51.10	$51.10
Purchase #7	$103.47	9.386%	$113.1817	$113.18	$113.20	$113.20
7 purchase totals =	$912.48		$978.5464	$978.55	$978.55	$978.50