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	$72.81	6.448%	$77.5048	$77.50	$77.50	$77.50
Purchase #2	$222.28	10.644%	$245.9395	$245.94	$245.95	$245.90
Purchase #3	$233.84	4.264%	$243.8109	$243.81	$243.80	$243.80
Purchase #4	$145.35	7.735%	$156.5928	$156.59	$156.60	$156.60
Purchase #5	$62.71	13.327%	$71.0674	$71.07	$71.05	$71.10
Purchase #6	$187.45	3.816%	$194.6031	$194.60	$194.60	$194.60
Purchase #7	$155.99	3.745%	$161.8318	$161.83	$161.85	$161.80
7 purchase totals =	$1,080.43		$1,151.3503	$1,151.34	$1,151.35	$1,151.30