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	$70.31	4.436%	$73.429	$73.43	$73.45	$73.40
Purchase #2	$181.94	7.133%	$194.9178	$194.92	$194.90	$194.90
Purchase #3	$80.76	12.558%	$90.9018	$90.90	$90.90	$90.90
Purchase #4	$220.90	6.524%	$235.3115	$235.31	$235.30	$235.30
Purchase #5	$52.81	7.534%	$56.7887	$56.79	$56.80	$56.80
Purchase #6	$75.71	10.764%	$83.8594	$83.86	$83.85	$83.90
Purchase #7	$40.59	7.654%	$43.6968	$43.70	$43.70	$43.70
7 purchase totals =	$723.02		$778.9050	$778.91	$778.90	$778.90