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	$151.30	3.693%	$156.8875	$156.89	$156.90	$156.90
Purchase #2	$226.90	12.484%	$255.2262	$255.23	$255.25	$255.20
Purchase #3	$216.30	3.387%	$223.6261	$223.63	$223.65	$223.60
Purchase #4	$47.30	9.292%	$51.6951	$51.70	$51.70	$51.70
Purchase #5	$144.62	12.233%	$162.3114	$162.31	$162.30	$162.30
Purchase #6	$28.85	10.373%	$31.8426	$31.84	$31.85	$31.80
Purchase #7	$91.68	6.241%	$97.4017	$97.40	$97.40	$97.40
7 purchase totals =	$906.95		$978.9906	$979.00	$979.05	$978.90