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	$54.46	9.792%	$59.7927	$59.79	$59.80	$59.80
Purchase #2	$103.67	11.148%	$115.2271	$115.23	$115.25	$115.20
Purchase #3	$237.65	7.843%	$256.2889	$256.29	$256.30	$256.30
Purchase #4	$201.81	3.528%	$208.9299	$208.93	$208.95	$208.90
Purchase #5	$145.96	3.705%	$151.3678	$151.37	$151.35	$151.40
Purchase #6	$233.43	3.709%	$242.0879	$242.09	$242.10	$242.10
Purchase #7	$142.40	9.179%	$155.4709	$155.47	$155.45	$155.50
7 purchase totals =	$1,119.38		$1,189.1652	$1,189.17	$1,189.20	$1,189.20