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	$34.91	8.617%	$37.9182	$37.92	$37.90	$37.90
Purchase #2	$217.59	9.192%	$237.5909	$237.59	$237.60	$237.60
Purchase #3	$241.94	7.419%	$259.8895	$259.89	$259.90	$259.90
Purchase #4	$100.86	4.465%	$105.3634	$105.36	$105.35	$105.40
Purchase #5	$126.91	9.384%	$138.8192	$138.82	$138.80	$138.80
Purchase #6	$25.79	9.314%	$28.1921	$28.19	$28.20	$28.20
Purchase #7	$195.84	13.692%	$222.6544	$222.65	$222.65	$222.70
7 purchase totals =	$943.84		$1,030.4277	$1,030.42	$1,030.40	$1,030.50