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	$65.59	8.303%	$71.0359	$71.04	$71.05	$71.00
Purchase #2	$198.87	12.365%	$223.4603	$223.46	$223.45	$223.50
Purchase #3	$16.87	11.748%	$18.8519	$18.85	$18.85	$18.90
Purchase #4	$46.44	13.275%	$52.6049	$52.60	$52.60	$52.60
Purchase #5	$138.38	13.462%	$157.0087	$157.01	$157.00	$157.00
Purchase #6	$70.93	11.303%	$78.9472	$78.95	$78.95	$78.90
Purchase #7	$44.88	6.252%	$47.6859	$47.69	$47.70	$47.70
7 purchase totals =	$581.96		$649.5948	$649.60	$649.60	$649.60