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	$70.45	9.546%	$77.1752	$77.18	$77.20	$77.20
Purchase #2	$42.63	5.206%	$44.8493	$44.85	$44.85	$44.80
Purchase #3	$160.51	8.747%	$174.5498	$174.55	$174.55	$174.50
Purchase #4	$109.38	5.689%	$115.6026	$115.60	$115.60	$115.60
Purchase #5	$205.81	11.455%	$229.3855	$229.39	$229.40	$229.40
Purchase #6	$46.61	11.364%	$51.9068	$51.91	$51.90	$51.90
Purchase #7	$76.92	11.102%	$85.4597	$85.46	$85.45	$85.50
7 purchase totals =	$712.31		$778.9289	$778.94	$778.95	$778.90