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	$163.32	6.859%	$174.5221	$174.52	$174.50	$174.50
Purchase #2	$226.59	8.798%	$246.5254	$246.53	$246.55	$246.50
Purchase #3	$36.45	9.293%	$39.8373	$39.84	$39.85	$39.80
Purchase #4	$53.70	6.645%	$57.2684	$57.27	$57.25	$57.30
Purchase #5	$126.94	9.841%	$139.4322	$139.43	$139.45	$139.40
Purchase #6	$76.60	7.386%	$82.2577	$82.26	$82.25	$82.30
Purchase #7	$136.78	4.498%	$142.9324	$142.93	$142.95	$142.90
7 purchase totals =	$820.38		$882.7755	$882.78	$882.80	$882.70