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	$229.31	8.821%	$249.5374	$249.54	$249.55	$249.50
Purchase #2	$25.78	13.159%	$29.1724	$29.17	$29.15	$29.20
Purchase #3	$43.94	5.552%	$46.3795	$46.38	$46.40	$46.40
Purchase #4	$12.97	6.733%	$13.8433	$13.84	$13.85	$13.80
Purchase #5	$110.89	7.868%	$119.6148	$119.61	$119.60	$119.60
Purchase #6	$161.79	3.737%	$167.8361	$167.84	$167.85	$167.80
Purchase #7	$40.40	6.236%	$42.9193	$42.92	$42.90	$42.90
7 purchase totals =	$625.08		$669.3028	$669.30	$669.30	$669.20