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	$35.40	9.618%	$38.8048	$38.80	$38.80	$38.80
Purchase #2	$126.44	7.822%	$136.3301	$136.33	$136.35	$136.30
Purchase #3	$132.85	13.265%	$150.4726	$150.47	$150.45	$150.50
Purchase #4	$37.43	9.349%	$40.9293	$40.93	$40.95	$40.90
Purchase #5	$249.59	9.442%	$273.1563	$273.16	$273.15	$273.20
Purchase #6	$176.90	3.181%	$182.5272	$182.53	$182.55	$182.50
Purchase #7	$230.74	6.158%	$244.949	$244.95	$244.95	$244.90
7 purchase totals =	$989.35		$1,067.1693	$1,067.17	$1,067.20	$1,067.10