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	$93.51	6.252%	$99.3562	$99.36	$99.35	$99.40
Purchase #2	$92.95	13.303%	$105.3151	$105.32	$105.30	$105.30
Purchase #3	$225.43	5.838%	$238.5906	$238.59	$238.60	$238.60
Purchase #4	$241.99	13.481%	$274.6127	$274.61	$274.60	$274.60
Purchase #5	$212.71	8.709%	$231.2349	$231.23	$231.25	$231.20
Purchase #6	$147.53	9.197%	$161.0983	$161.10	$161.10	$161.10
Purchase #7	$97.99	13.715%	$111.4293	$111.43	$111.45	$111.40
7 purchase totals =	$1,112.11		$1,221.6371	$1,221.64	$1,221.65	$1,221.60