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	$81.48	5.329%	$85.8221	$85.82	$85.80	$85.80
Purchase #2	$240.61	3.659%	$249.4139	$249.41	$249.40	$249.40
Purchase #3	$120.65	13.533%	$136.9776	$136.98	$137.00	$137.00
Purchase #4	$37.63	8.802%	$40.9422	$40.94	$40.95	$40.90
Purchase #5	$166.90	4.547%	$174.4889	$174.49	$174.50	$174.50
Purchase #6	$205.57	6.171%	$218.2557	$218.26	$218.25	$218.30
Purchase #7	$192.35	13.352%	$218.0326	$218.03	$218.05	$218.00
7 purchase totals =	$1,045.19		$1,123.9330	$1,123.93	$1,123.95	$1,123.90