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	$24.29	13.661%	$27.6083	$27.61	$27.60	$27.60
Purchase #2	$223.84	6.548%	$238.497	$238.50	$238.50	$238.50
Purchase #3	$32.89	8.587%	$35.7143	$35.71	$35.70	$35.70
Purchase #4	$232.59	3.454%	$240.6237	$240.62	$240.60	$240.60
Purchase #5	$128.84	4.837%	$135.072	$135.07	$135.05	$135.10
Purchase #6	$126.90	12.229%	$142.4186	$142.42	$142.40	$142.40
Purchase #7	$231.77	5.533%	$244.5938	$244.59	$244.60	$244.60
7 purchase totals =	$1,001.12		$1,064.5277	$1,064.52	$1,064.45	$1,064.50