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	$247.40	12.293%	$277.8129	$277.81	$277.80	$277.80
Purchase #2	$117.76	12.206%	$132.1338	$132.13	$132.15	$132.10
Purchase #3	$98.75	11.285%	$109.8939	$109.89	$109.90	$109.90
Purchase #4	$36.52	9.515%	$39.9949	$39.99	$40.00	$40.00
Purchase #5	$170.32	11.777%	$190.3786	$190.38	$190.40	$190.40
Purchase #6	$149.67	4.786%	$156.8332	$156.83	$156.85	$156.80
Purchase #7	$96.78	5.825%	$102.4174	$102.42	$102.40	$102.40
7 purchase totals =	$917.20		$1,009.4647	$1,009.45	$1,009.50	$1,009.40