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	$102.54	4.188%	$106.8344	$106.83	$106.85	$106.80
Purchase #2	$143.99	9.106%	$157.1017	$157.10	$157.10	$157.10
Purchase #3	$49.67	9.657%	$54.4666	$54.47	$54.45	$54.50
Purchase #4	$94.90	3.706%	$98.417	$98.42	$98.40	$98.40
Purchase #5	$100.42	4.662%	$105.1016	$105.10	$105.10	$105.10
Purchase #6	$27.56	13.430%	$31.2613	$31.26	$31.25	$31.30
Purchase #7	$38.59	12.300%	$43.3366	$43.34	$43.35	$43.30
7 purchase totals =	$557.67		$596.5192	$596.52	$596.50	$596.50