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	$66.82	5.286%	$70.3521	$70.35	$70.35	$70.40
Purchase #2	$95.37	4.575%	$99.7332	$99.73	$99.75	$99.70
Purchase #3	$190.73	13.264%	$216.0284	$216.03	$216.05	$216.00
Purchase #4	$148.65	7.533%	$159.8478	$159.85	$159.85	$159.80
Purchase #5	$207.33	12.398%	$233.0348	$233.03	$233.05	$233.00
Purchase #6	$27.71	12.438%	$31.1566	$31.16	$31.15	$31.20
Purchase #7	$119.92	9.254%	$131.0174	$131.02	$131.00	$131.00
7 purchase totals =	$856.53		$941.1703	$941.17	$941.20	$941.10