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	$83.26	12.181%	$93.4019	$93.40	$93.40	$93.40
Purchase #2	$42.80	10.267%	$47.1943	$47.19	$47.20	$47.20
Purchase #3	$175.52	4.160%	$182.8216	$182.82	$182.80	$182.80
Purchase #4	$114.56	4.401%	$119.6018	$119.60	$119.60	$119.60
Purchase #5	$38.82	5.242%	$40.8549	$40.85	$40.85	$40.90
Purchase #6	$118.96	3.755%	$123.4269	$123.43	$123.45	$123.40
Purchase #7	$123.34	6.221%	$131.013	$131.01	$131.00	$131.00
7 purchase totals =	$697.26		$738.3144	$738.30	$738.30	$738.30