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	$167.33	12.701%	$188.5826	$188.58	$188.60	$188.60
Purchase #2	$232.67	4.846%	$243.9452	$243.95	$243.95	$243.90
Purchase #3	$50.26	3.135%	$51.8357	$51.84	$51.85	$51.80
Purchase #4	$123.46	11.490%	$137.6456	$137.65	$137.65	$137.60
Purchase #5	$78.72	13.856%	$89.6274	$89.63	$89.65	$89.60
Purchase #6	$18.29	10.801%	$20.2655	$20.27	$20.25	$20.30
Purchase #7	$43.59	7.239%	$46.7455	$46.75	$46.75	$46.70
7 purchase totals =	$714.32		$778.6475	$778.67	$778.70	$778.50