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	$120.69	6.219%	$128.1957	$128.20	$128.20	$128.20
Purchase #2	$62.66	4.726%	$65.6213	$65.62	$65.60	$65.60
Purchase #3	$76.57	8.473%	$83.0578	$83.06	$83.05	$83.10
Purchase #4	$156.46	10.209%	$172.433	$172.43	$172.45	$172.40
Purchase #5	$112.66	7.853%	$121.5072	$121.51	$121.50	$121.50
Purchase #6	$217.70	7.137%	$233.2372	$233.24	$233.25	$233.20
Purchase #7	$184.76	6.369%	$196.5274	$196.53	$196.55	$196.50
7 purchase totals =	$931.50		$1,000.5796	$1,000.59	$1,000.60	$1,000.50