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	$35.55	9.716%	$39.004	$39.00	$39.00	$39.00
Purchase #2	$25.50	12.479%	$28.6821	$28.68	$28.70	$28.70
Purchase #3	$38.51	13.823%	$43.8332	$43.83	$43.85	$43.80
Purchase #4	$136.76	6.223%	$145.2706	$145.27	$145.25	$145.30
Purchase #5	$210.79	8.512%	$228.7324	$228.73	$228.75	$228.70
Purchase #6	$227.40	12.459%	$255.7318	$255.73	$255.75	$255.70
Purchase #7	$47.81	5.828%	$50.5964	$50.60	$50.60	$50.60
7 purchase totals =	$722.32		$791.8505	$791.84	$791.90	$791.80