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	$233.31	9.504%	$255.4838	$255.48	$255.50	$255.50
Purchase #2	$86.70	12.858%	$97.8479	$97.85	$97.85	$97.80
Purchase #3	$145.91	8.544%	$158.3766	$158.38	$158.40	$158.40
Purchase #4	$200.85	13.139%	$227.2397	$227.24	$227.25	$227.20
Purchase #5	$200.29	9.200%	$218.7167	$218.72	$218.70	$218.70
Purchase #6	$177.99	3.111%	$183.5273	$183.53	$183.55	$183.50
Purchase #7	$136.75	11.395%	$152.3327	$152.33	$152.35	$152.30
7 purchase totals =	$1,181.80		$1,293.5247	$1,293.53	$1,293.60	$1,293.40