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	$75.76	7.611%	$81.5261	$81.53	$81.55	$81.50
Purchase #2	$73.50	9.595%	$80.5523	$80.55	$80.55	$80.60
Purchase #3	$215.66	11.469%	$240.394	$240.39	$240.40	$240.40
Purchase #4	$169.37	10.714%	$187.5163	$187.52	$187.50	$187.50
Purchase #5	$169.66	5.415%	$178.8471	$178.85	$178.85	$178.80
Purchase #6	$131.78	8.141%	$142.5082	$142.51	$142.50	$142.50
Purchase #7	$10.65	8.190%	$11.5222	$11.52	$11.50	$11.50
7 purchase totals =	$846.38		$922.8662	$922.87	$922.85	$922.80