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	$49.66	12.322%	$55.7791	$55.78	$55.80	$55.80
Purchase #2	$201.53	13.797%	$229.3351	$229.34	$229.35	$229.30
Purchase #3	$166.75	8.189%	$180.4052	$180.41	$180.40	$180.40
Purchase #4	$244.44	12.832%	$275.8065	$275.81	$275.80	$275.80
Purchase #5	$155.81	5.351%	$164.1474	$164.15	$164.15	$164.10
Purchase #6	$116.65	9.232%	$127.4191	$127.42	$127.40	$127.40
Purchase #7	$212.55	4.706%	$222.5526	$222.55	$222.55	$222.60
7 purchase totals =	$1,147.39		$1,255.4450	$1,255.46	$1,255.45	$1,255.40