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	$18.86	10.726%	$20.8829	$20.88	$20.90	$20.90
Purchase #2	$240.60	7.589%	$258.8591	$258.86	$258.85	$258.90
Purchase #3	$111.44	9.874%	$122.4436	$122.44	$122.45	$122.40
Purchase #4	$144.53	12.447%	$162.5196	$162.52	$162.50	$162.50
Purchase #5	$240.93	10.142%	$265.3651	$265.37	$265.35	$265.40
Purchase #6	$48.54	12.171%	$54.4478	$54.45	$54.45	$54.40
Purchase #7	$198.65	10.759%	$220.0228	$220.02	$220.00	$220.00
7 purchase totals =	$1,003.55		$1,104.5409	$1,104.54	$1,104.50	$1,104.50