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	$135.47	12.497%	$152.3997	$152.40	$152.40	$152.40
Purchase #2	$34.46	11.823%	$38.5342	$38.53	$38.55	$38.50
Purchase #3	$103.39	11.722%	$115.5094	$115.51	$115.50	$115.50
Purchase #4	$227.83	6.747%	$243.2017	$243.20	$243.20	$243.20
Purchase #5	$115.57	4.289%	$120.5268	$120.53	$120.55	$120.50
Purchase #6	$246.34	3.345%	$254.5801	$254.58	$254.60	$254.60
Purchase #7	$107.33	3.749%	$111.3538	$111.35	$111.35	$111.40
7 purchase totals =	$970.39		$1,036.1057	$1,036.10	$1,036.15	$1,036.10