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	$241.92	9.792%	$265.6088	$265.61	$265.60	$265.60
Purchase #2	$84.49	6.863%	$90.2885	$90.29	$90.30	$90.30
Purchase #3	$238.59	6.389%	$253.8335	$253.83	$253.85	$253.80
Purchase #4	$110.90	13.414%	$125.7761	$125.78	$125.80	$125.80
Purchase #5	$186.55	7.633%	$200.7894	$200.79	$200.80	$200.80
Purchase #6	$13.44	8.452%	$14.5759	$14.58	$14.60	$14.60
Purchase #7	$31.55	4.326%	$32.9149	$32.91	$32.90	$32.90
7 purchase totals =	$907.44		$983.7871	$983.79	$983.85	$983.80