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	$72.32	8.828%	$78.7044	$78.70	$78.70	$78.70
Purchase #2	$81.76	4.792%	$85.6779	$85.68	$85.70	$85.70
Purchase #3	$6.44	7.279%	$6.9088	$6.91	$6.90	$6.90
Purchase #4	$109.61	3.625%	$113.5834	$113.58	$113.60	$113.60
Purchase #5	$105.69	11.187%	$117.5135	$117.51	$117.50	$117.50
Purchase #6	$168.93	9.516%	$185.0054	$185.01	$185.00	$185.00
Purchase #7	$120.72	8.591%	$131.0911	$131.09	$131.10	$131.10
7 purchase totals =	$665.47		$718.4845	$718.48	$718.50	$718.50