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	$116.28	6.535%	$123.8789	$123.88	$123.90	$123.90
Purchase #2	$101.46	11.512%	$113.1401	$113.14	$113.15	$113.10
Purchase #3	$209.77	11.175%	$233.2118	$233.21	$233.20	$233.20
Purchase #4	$242.75	9.738%	$266.389	$266.39	$266.40	$266.40
Purchase #5	$164.96	13.134%	$186.6258	$186.63	$186.65	$186.60
Purchase #6	$245.35	5.809%	$259.6024	$259.60	$259.60	$259.60
Purchase #7	$90.51	11.395%	$100.8236	$100.82	$100.80	$100.80
7 purchase totals =	$1,171.08		$1,283.6716	$1,283.67	$1,283.70	$1,283.60