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	$86.55	3.512%	$89.5896	$89.59	$89.60	$89.60
Purchase #2	$92.81	11.496%	$103.4794	$103.48	$103.50	$103.50
Purchase #3	$242.30	12.546%	$272.699	$272.70	$272.70	$272.70
Purchase #4	$119.53	6.682%	$127.517	$127.52	$127.50	$127.50
Purchase #5	$150.58	13.849%	$171.4338	$171.43	$171.45	$171.40
Purchase #6	$212.64	10.298%	$234.5377	$234.54	$234.55	$234.50
Purchase #7	$187.54	6.561%	$199.8445	$199.84	$199.85	$199.80
7 purchase totals =	$1,091.95		$1,199.1010	$1,199.10	$1,199.15	$1,199.00