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	$231.56	11.684%	$258.6155	$258.62	$258.60	$258.60
Purchase #2	$71.43	6.553%	$76.1108	$76.11	$76.10	$76.10
Purchase #3	$185.77	6.703%	$198.2222	$198.22	$198.20	$198.20
Purchase #4	$144.48	9.534%	$158.2547	$158.25	$158.25	$158.30
Purchase #5	$36.36	10.366%	$40.1291	$40.13	$40.15	$40.10
Purchase #6	$51.99	8.648%	$56.4861	$56.49	$56.50	$56.50
Purchase #7	$38.52	10.701%	$42.642	$42.64	$42.65	$42.60
7 purchase totals =	$760.11		$830.4604	$830.46	$830.45	$830.40