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	$83.27	7.620%	$89.6152	$89.62	$89.60	$89.60
Purchase #2	$96.27	12.289%	$108.1006	$108.10	$108.10	$108.10
Purchase #3	$201.46	8.849%	$219.2872	$219.29	$219.30	$219.30
Purchase #4	$164.29	10.456%	$181.4682	$181.47	$181.45	$181.50
Purchase #5	$82.29	5.679%	$86.9632	$86.96	$86.95	$87.00
Purchase #6	$189.71	10.151%	$208.9675	$208.97	$208.95	$209.00
Purchase #7	$79.46	13.264%	$89.9996	$90.00	$90.00	$90.00
7 purchase totals =	$896.75		$984.4015	$984.41	$984.35	$984.50