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	$70.64	11.114%	$78.4909	$78.49	$78.50	$78.50
Purchase #2	$62.55	13.604%	$71.0593	$71.06	$71.05	$71.10
Purchase #3	$62.64	4.314%	$65.3423	$65.34	$65.35	$65.30
Purchase #4	$158.77	6.397%	$168.9265	$168.93	$168.95	$168.90
Purchase #5	$236.43	6.408%	$251.5804	$251.58	$251.60	$251.60
Purchase #6	$75.75	8.146%	$81.9206	$81.92	$81.90	$81.90
Purchase #7	$104.79	12.448%	$117.8343	$117.83	$117.85	$117.80
7 purchase totals =	$771.57		$835.1543	$835.15	$835.20	$835.10