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	$93.57	12.447%	$105.2167	$105.22	$105.20	$105.20
Purchase #2	$51.50	5.641%	$54.4051	$54.41	$54.40	$54.40
Purchase #3	$19.40	5.582%	$20.4829	$20.48	$20.50	$20.50
Purchase #4	$199.61	13.193%	$225.9445	$225.94	$225.95	$225.90
Purchase #5	$42.40	9.782%	$46.5476	$46.55	$46.55	$46.50
Purchase #6	$186.59	11.809%	$208.6244	$208.62	$208.60	$208.60
Purchase #7	$240.85	10.703%	$266.6282	$266.63	$266.65	$266.60
7 purchase totals =	$833.92		$927.8494	$927.85	$927.85	$927.70