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	$191.90	9.458%	$210.0499	$210.05	$210.05	$210.00
Purchase #2	$99.61	3.595%	$103.191	$103.19	$103.20	$103.20
Purchase #3	$142.69	11.295%	$158.8068	$158.81	$158.80	$158.80
Purchase #4	$109.64	4.484%	$114.5563	$114.56	$114.55	$114.60
Purchase #5	$140.85	12.760%	$158.8225	$158.82	$158.80	$158.80
Purchase #6	$200.85	7.619%	$216.1528	$216.15	$216.15	$216.20
Purchase #7	$14.82	12.716%	$16.7045	$16.70	$16.70	$16.70
7 purchase totals =	$900.36		$978.2838	$978.28	$978.25	$978.30