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	$55.33	3.866%	$57.4691	$57.47	$57.45	$57.50
Purchase #2	$73.68	11.302%	$82.0073	$82.01	$82.00	$82.00
Purchase #3	$29.93	12.248%	$33.5958	$33.60	$33.60	$33.60
Purchase #4	$155.69	11.788%	$174.0427	$174.04	$174.05	$174.00
Purchase #5	$211.62	9.591%	$231.9165	$231.92	$231.90	$231.90
Purchase #6	$73.53	8.800%	$80.0006	$80.00	$80.00	$80.00
Purchase #7	$59.80	11.259%	$66.5329	$66.53	$66.55	$66.50
7 purchase totals =	$659.58		$725.5649	$725.57	$725.55	$725.50