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	$165.74	11.557%	$184.8946	$184.89	$184.90	$184.90
Purchase #2	$118.91	12.269%	$133.4991	$133.50	$133.50	$133.50
Purchase #3	$89.61	12.253%	$100.5899	$100.59	$100.60	$100.60
Purchase #4	$56.90	11.173%	$63.2574	$63.26	$63.25	$63.30
Purchase #5	$153.43	9.226%	$167.5855	$167.59	$167.60	$167.60
Purchase #6	$233.34	5.831%	$246.9461	$246.95	$246.95	$246.90
Purchase #7	$64.74	9.393%	$70.821	$70.82	$70.80	$70.80
7 purchase totals =	$882.67		$967.5936	$967.60	$967.60	$967.60