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	$50.70	9.465%	$55.4988	$55.50	$55.50	$55.50
Purchase #2	$64.70	3.851%	$67.1916	$67.19	$67.20	$67.20
Purchase #3	$248.36	13.786%	$282.5989	$282.60	$282.60	$282.60
Purchase #4	$197.50	11.141%	$219.5035	$219.50	$219.50	$219.50
Purchase #5	$175.91	8.265%	$190.449	$190.45	$190.45	$190.40
Purchase #6	$138.97	10.212%	$153.1616	$153.16	$153.15	$153.20
Purchase #7	$182.41	7.661%	$196.3844	$196.38	$196.40	$196.40
7 purchase totals =	$1,058.55		$1,164.7878	$1,164.78	$1,164.80	$1,164.80