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	$36.86	10.158%	$40.6042	$40.60	$40.60	$40.60
Purchase #2	$110.34	5.830%	$116.7728	$116.77	$116.75	$116.80
Purchase #3	$82.86	13.534%	$94.0743	$94.07	$94.05	$94.10
Purchase #4	$206.44	5.430%	$217.6497	$217.65	$217.65	$217.60
Purchase #5	$199.70	9.103%	$217.8787	$217.88	$217.90	$217.90
Purchase #6	$125.94	12.760%	$142.0099	$142.01	$142.00	$142.00
Purchase #7	$244.47	4.240%	$254.8355	$254.84	$254.85	$254.80
7 purchase totals =	$1,006.61		$1,083.8251	$1,083.82	$1,083.80	$1,083.80