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	$239.96	9.758%	$263.3753	$263.38	$263.40	$263.40
Purchase #2	$81.57	12.423%	$91.7034	$91.70	$91.70	$91.70
Purchase #3	$174.35	5.270%	$183.5382	$183.54	$183.55	$183.50
Purchase #4	$133.50	7.783%	$143.8903	$143.89	$143.90	$143.90
Purchase #5	$130.56	12.317%	$146.6411	$146.64	$146.65	$146.60
Purchase #6	$45.51	6.636%	$48.53	$48.53	$48.55	$48.50
Purchase #7	$27.60	4.418%	$28.8194	$28.82	$28.80	$28.80
7 purchase totals =	$833.05		$906.4977	$906.50	$906.55	$906.40