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	$239.95	13.198%	$271.6186	$271.62	$271.60	$271.60
Purchase #2	$35.69	5.811%	$37.7639	$37.76	$37.75	$37.80
Purchase #3	$163.82	3.145%	$168.9721	$168.97	$168.95	$169.00
Purchase #4	$54.97	13.849%	$62.5828	$62.58	$62.60	$62.60
Purchase #5	$95.94	4.532%	$100.288	$100.29	$100.30	$100.30
Purchase #6	$202.95	9.810%	$222.8594	$222.86	$222.85	$222.90
Purchase #7	$98.45	7.678%	$106.009	$106.01	$106.00	$106.00
7 purchase totals =	$891.77		$970.0938	$970.09	$970.05	$970.20