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	$185.39	12.709%	$208.9512	$208.95	$208.95	$209.00
Purchase #2	$111.37	10.719%	$123.3078	$123.31	$123.30	$123.30
Purchase #3	$80.48	10.115%	$88.6206	$88.62	$88.60	$88.60
Purchase #4	$232.92	6.189%	$247.3354	$247.34	$247.35	$247.30
Purchase #5	$191.89	4.552%	$200.6248	$200.62	$200.60	$200.60
Purchase #6	$120.72	8.467%	$130.9414	$130.94	$130.95	$130.90
Purchase #7	$105.89	12.839%	$119.4852	$119.49	$119.50	$119.50
7 purchase totals =	$1,028.66		$1,119.2664	$1,119.27	$1,119.25	$1,119.20