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	$96.49	3.531%	$99.8971	$99.90	$99.90	$99.90
Purchase #2	$38.39	6.605%	$40.9257	$40.93	$40.95	$40.90
Purchase #3	$122.27	12.520%	$137.5782	$137.58	$137.60	$137.60
Purchase #4	$143.46	9.299%	$156.8003	$156.80	$156.80	$156.80
Purchase #5	$234.37	9.771%	$257.2703	$257.27	$257.25	$257.30
Purchase #6	$196.27	13.673%	$223.106	$223.11	$223.10	$223.10
Purchase #7	$40.96	12.317%	$46.005	$46.01	$46.00	$46.00
7 purchase totals =	$872.21		$961.5826	$961.60	$961.60	$961.60