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	$169.51	6.362%	$180.2942	$180.29	$180.30	$180.30
Purchase #2	$95.71	11.600%	$106.8124	$106.81	$106.80	$106.80
Purchase #3	$124.86	3.191%	$128.8443	$128.84	$128.85	$128.80
Purchase #4	$166.90	9.590%	$182.9057	$182.91	$182.90	$182.90
Purchase #5	$241.91	7.693%	$260.5201	$260.52	$260.50	$260.50
Purchase #6	$130.33	7.870%	$140.587	$140.59	$140.60	$140.60
Purchase #7	$10.67	11.867%	$11.9362	$11.94	$11.95	$11.90
7 purchase totals =	$939.89		$1,011.8999	$1,011.90	$1,011.90	$1,011.80