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	$182.53	5.236%	$192.0873	$192.09	$192.10	$192.10
Purchase #2	$131.61	10.506%	$145.4369	$145.44	$145.45	$145.40
Purchase #3	$225.27	11.840%	$251.942	$251.94	$251.95	$251.90
Purchase #4	$41.85	3.784%	$43.4336	$43.43	$43.45	$43.40
Purchase #5	$63.48	11.604%	$70.8462	$70.85	$70.85	$70.80
Purchase #6	$35.55	11.416%	$39.6084	$39.61	$39.60	$39.60
Purchase #7	$82.80	9.709%	$90.8391	$90.84	$90.85	$90.80
7 purchase totals =	$763.09		$834.1935	$834.20	$834.25	$834.00