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	$88.33	13.430%	$100.1927	$100.19	$100.20	$100.20
Purchase #2	$50.53	8.518%	$54.8341	$54.83	$54.85	$54.80
Purchase #3	$213.31	9.781%	$234.1739	$234.17	$234.15	$234.20
Purchase #4	$123.93	13.240%	$140.3383	$140.34	$140.35	$140.30
Purchase #5	$109.71	4.388%	$114.5241	$114.52	$114.50	$114.50
Purchase #6	$107.93	9.706%	$118.4057	$118.41	$118.40	$118.40
Purchase #7	$197.28	7.849%	$212.7645	$212.76	$212.75	$212.80
7 purchase totals =	$891.02		$975.2333	$975.22	$975.20	$975.20