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	$118.77	3.810%	$123.2951	$123.30	$123.30	$123.30
Purchase #2	$95.84	9.472%	$104.918	$104.92	$104.90	$104.90
Purchase #3	$196.32	6.396%	$208.8766	$208.88	$208.90	$208.90
Purchase #4	$8.45	3.188%	$8.7194	$8.72	$8.70	$8.70
Purchase #5	$69.46	12.780%	$78.337	$78.34	$78.35	$78.30
Purchase #6	$246.96	6.531%	$263.089	$263.09	$263.10	$263.10
Purchase #7	$154.36	3.525%	$159.8012	$159.80	$159.80	$159.80
7 purchase totals =	$890.16		$947.0363	$947.05	$947.05	$947.00