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	$248.93	8.503%	$270.0965	$270.10	$270.10	$270.10
Purchase #2	$131.97	11.179%	$146.7229	$146.72	$146.70	$146.70
Purchase #3	$149.54	9.481%	$163.7179	$163.72	$163.70	$163.70
Purchase #4	$76.53	7.222%	$82.057	$82.06	$82.05	$82.10
Purchase #5	$247.36	3.337%	$255.6144	$255.61	$255.60	$255.60
Purchase #6	$43.28	5.866%	$45.8188	$45.82	$45.80	$45.80
Purchase #7	$31.78	6.419%	$33.82	$33.82	$33.80	$33.80
7 purchase totals =	$929.39		$997.8475	$997.85	$997.75	$997.80