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	$32.57	12.347%	$36.5914	$36.59	$36.60	$36.60
Purchase #2	$246.32	4.117%	$256.461	$256.46	$256.45	$256.50
Purchase #3	$179.83	3.167%	$185.5252	$185.53	$185.55	$185.50
Purchase #4	$239.31	6.640%	$255.2002	$255.20	$255.20	$255.20
Purchase #5	$180.25	3.323%	$186.2397	$186.24	$186.25	$186.20
Purchase #6	$168.95	8.189%	$182.7853	$182.79	$182.80	$182.80
Purchase #7	$148.92	11.356%	$165.8314	$165.83	$165.85	$165.80
7 purchase totals =	$1,196.15		$1,268.6342	$1,268.64	$1,268.70	$1,268.60