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	$184.90	13.170%	$209.2513	$209.25	$209.25	$209.30
Purchase #2	$53.44	7.176%	$57.2749	$57.27	$57.25	$57.30
Purchase #3	$38.50	4.511%	$40.2367	$40.24	$40.25	$40.20
Purchase #4	$212.78	11.353%	$236.9369	$236.94	$236.95	$236.90
Purchase #5	$214.91	3.543%	$222.5243	$222.52	$222.50	$222.50
Purchase #6	$208.54	12.596%	$234.8077	$234.81	$234.80	$234.80
Purchase #7	$247.69	12.860%	$279.5429	$279.54	$279.55	$279.50
7 purchase totals =	$1,160.76		$1,280.5747	$1,280.57	$1,280.55	$1,280.50