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	$245.71	11.233%	$273.3106	$273.31	$273.30	$273.30
Purchase #2	$97.68	8.788%	$106.2641	$106.26	$106.25	$106.30
Purchase #3	$114.47	7.641%	$123.2167	$123.22	$123.20	$123.20
Purchase #4	$131.85	9.351%	$144.1793	$144.18	$144.20	$144.20
Purchase #5	$120.57	13.443%	$136.7782	$136.78	$136.80	$136.80
Purchase #6	$37.59	13.683%	$42.7334	$42.73	$42.75	$42.70
Purchase #7	$119.89	13.791%	$136.424	$136.42	$136.40	$136.40
7 purchase totals =	$867.76		$962.9063	$962.90	$962.90	$962.90