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	$160.72	3.556%	$166.4352	$166.44	$166.45	$166.40
Purchase #2	$196.58	6.290%	$208.9449	$208.94	$208.95	$208.90
Purchase #3	$231.93	11.389%	$258.3445	$258.34	$258.35	$258.30
Purchase #4	$186.33	5.324%	$196.2502	$196.25	$196.25	$196.30
Purchase #5	$35.94	9.668%	$39.4147	$39.41	$39.40	$39.40
Purchase #6	$100.44	12.380%	$112.8745	$112.87	$112.85	$112.90
Purchase #7	$94.41	9.574%	$103.4488	$103.45	$103.45	$103.40
7 purchase totals =	$1,006.35		$1,085.7128	$1,085.70	$1,085.70	$1,085.60