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	$242.32	3.786%	$251.4942	$251.49	$251.50	$251.50
Purchase #2	$223.54	6.375%	$237.7907	$237.79	$237.80	$237.80
Purchase #3	$208.61	6.791%	$222.7767	$222.78	$222.80	$222.80
Purchase #4	$189.87	5.248%	$199.8344	$199.83	$199.85	$199.80
Purchase #5	$123.85	4.719%	$129.6945	$129.69	$129.70	$129.70
Purchase #6	$194.51	3.189%	$200.7129	$200.71	$200.70	$200.70
Purchase #7	$33.95	10.857%	$37.636	$37.64	$37.65	$37.60
7 purchase totals =	$1,216.65		$1,279.9394	$1,279.93	$1,280.00	$1,279.90