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	$11.37	3.746%	$11.7959	$11.80	$11.80	$11.80
Purchase #2	$78.55	7.379%	$84.3462	$84.35	$84.35	$84.30
Purchase #3	$139.54	13.637%	$158.5691	$158.57	$158.55	$158.60
Purchase #4	$133.62	4.402%	$139.502	$139.50	$139.50	$139.50
Purchase #5	$82.87	7.396%	$88.9991	$89.00	$89.00	$89.00
Purchase #6	$57.53	3.453%	$59.5165	$59.52	$59.50	$59.50
Purchase #7	$167.30	6.770%	$178.6262	$178.63	$178.65	$178.60
7 purchase totals =	$670.78		$721.3550	$721.37	$721.35	$721.30