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	$209.78	6.242%	$222.8745	$222.87	$222.85	$222.90
Purchase #2	$77.58	7.591%	$83.4691	$83.47	$83.45	$83.50
Purchase #3	$233.72	3.337%	$241.5192	$241.52	$241.50	$241.50
Purchase #4	$226.78	5.108%	$238.3639	$238.36	$238.35	$238.40
Purchase #5	$125.85	12.271%	$141.2931	$141.29	$141.30	$141.30
Purchase #6	$246.99	6.870%	$263.9582	$263.96	$263.95	$264.00
Purchase #7	$117.99	9.241%	$128.8935	$128.89	$128.90	$128.90
7 purchase totals =	$1,238.69		$1,320.3715	$1,320.36	$1,320.30	$1,320.50