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	$25.54	9.458%	$27.9556	$27.96	$27.95	$28.00
Purchase #2	$152.66	12.392%	$171.5776	$171.58	$171.60	$171.60
Purchase #3	$39.76	6.315%	$42.2708	$42.27	$42.25	$42.30
Purchase #4	$152.47	5.436%	$160.7583	$160.76	$160.75	$160.80
Purchase #5	$213.43	10.558%	$235.9639	$235.96	$235.95	$236.00
Purchase #6	$162.58	10.509%	$179.6655	$179.67	$179.65	$179.70
Purchase #7	$45.37	13.531%	$51.509	$51.51	$51.50	$51.50
7 purchase totals =	$791.81		$869.7007	$869.71	$869.65	$869.90