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	$108.25	13.141%	$122.4751	$122.48	$122.50	$122.50
Purchase #2	$214.47	10.687%	$237.3904	$237.39	$237.40	$237.40
Purchase #3	$116.58	12.525%	$131.1816	$131.18	$131.20	$131.20
Purchase #4	$117.98	4.399%	$123.1699	$123.17	$123.15	$123.20
Purchase #5	$89.25	10.320%	$98.4606	$98.46	$98.45	$98.50
Purchase #6	$181.45	11.344%	$202.0337	$202.03	$202.05	$202.00
Purchase #7	$169.51	12.579%	$190.8327	$190.83	$190.85	$190.80
7 purchase totals =	$997.49		$1,105.5440	$1,105.54	$1,105.60	$1,105.60