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	$52.86	4.561%	$55.2709	$55.27	$55.25	$55.30
Purchase #2	$226.35	13.829%	$257.6519	$257.65	$257.65	$257.70
Purchase #3	$63.59	10.664%	$70.3712	$70.37	$70.35	$70.40
Purchase #4	$119.39	11.260%	$132.8333	$132.83	$132.85	$132.80
Purchase #5	$27.95	12.870%	$31.5472	$31.55	$31.55	$31.50
Purchase #6	$85.39	4.233%	$89.0046	$89.00	$89.00	$89.00
Purchase #7	$103.87	6.407%	$110.525	$110.53	$110.55	$110.50
7 purchase totals =	$679.40		$747.2041	$747.20	$747.20	$747.20