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	$78.58	13.264%	$89.0029	$89.00	$89.00	$89.00
Purchase #2	$28.59	10.515%	$31.5962	$31.60	$31.60	$31.60
Purchase #3	$169.40	6.663%	$180.6871	$180.69	$180.70	$180.70
Purchase #4	$213.80	9.417%	$233.9335	$233.93	$233.95	$233.90
Purchase #5	$108.56	4.518%	$113.4647	$113.46	$113.45	$113.50
Purchase #6	$228.87	5.456%	$241.3571	$241.36	$241.35	$241.40
Purchase #7	$199.82	9.625%	$219.0527	$219.05	$219.05	$219.10
7 purchase totals =	$1,027.62		$1,109.0942	$1,109.09	$1,109.10	$1,109.20