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	$67.48	4.366%	$70.4262	$70.43	$70.45	$70.40
Purchase #2	$148.25	10.660%	$164.0535	$164.05	$164.05	$164.10
Purchase #3	$116.35	6.651%	$124.0884	$124.09	$124.10	$124.10
Purchase #4	$114.47	8.343%	$124.0202	$124.02	$124.00	$124.00
Purchase #5	$169.33	11.305%	$188.4728	$188.47	$188.45	$188.50
Purchase #6	$76.90	5.182%	$80.885	$80.89	$80.90	$80.90
Purchase #7	$178.38	6.233%	$189.4984	$189.50	$189.50	$189.50
7 purchase totals =	$871.16		$941.4445	$941.45	$941.45	$941.50