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	$103.43	8.746%	$112.476	$112.48	$112.50	$112.50
Purchase #2	$150.42	8.576%	$163.32	$163.32	$163.30	$163.30
Purchase #3	$214.46	13.598%	$243.6223	$243.62	$243.60	$243.60
Purchase #4	$161.38	4.172%	$168.1128	$168.11	$168.10	$168.10
Purchase #5	$216.64	11.488%	$241.5276	$241.53	$241.55	$241.50
Purchase #6	$35.83	6.218%	$38.0579	$38.06	$38.05	$38.10
Purchase #7	$241.59	5.706%	$255.3751	$255.38	$255.40	$255.40
7 purchase totals =	$1,123.75		$1,222.4917	$1,222.50	$1,222.50	$1,222.50