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	$108.62	13.311%	$123.0784	$123.08	$123.10	$123.10
Purchase #2	$156.85	7.471%	$168.5683	$168.57	$168.55	$168.60
Purchase #3	$38.98	6.531%	$41.5258	$41.53	$41.55	$41.50
Purchase #4	$108.73	3.856%	$112.9226	$112.92	$112.90	$112.90
Purchase #5	$243.64	5.440%	$256.894	$256.89	$256.90	$256.90
Purchase #6	$32.97	10.314%	$36.3705	$36.37	$36.35	$36.40
Purchase #7	$52.26	12.823%	$58.9613	$58.96	$58.95	$59.00
7 purchase totals =	$742.05		$798.3209	$798.32	$798.30	$798.40