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	$72.58	10.693%	$80.341	$80.34	$80.35	$80.30
Purchase #2	$246.85	13.642%	$280.5253	$280.53	$280.55	$280.50
Purchase #3	$36.53	10.394%	$40.3269	$40.33	$40.35	$40.30
Purchase #4	$171.71	5.486%	$181.13	$181.13	$181.15	$181.10
Purchase #5	$57.60	11.746%	$64.3657	$64.37	$64.35	$64.40
Purchase #6	$210.85	9.523%	$230.9292	$230.93	$230.95	$230.90
Purchase #7	$149.47	10.741%	$165.5246	$165.52	$165.50	$165.50
7 purchase totals =	$945.59		$1,043.1427	$1,043.15	$1,043.20	$1,043.00