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	$210.54	5.153%	$221.3891	$221.39	$221.40	$221.40
Purchase #2	$192.68	3.421%	$199.2716	$199.27	$199.25	$199.30
Purchase #3	$190.59	3.150%	$196.5936	$196.59	$196.60	$196.60
Purchase #4	$32.37	12.767%	$36.5027	$36.50	$36.50	$36.50
Purchase #5	$121.98	9.466%	$133.5266	$133.53	$133.55	$133.50
Purchase #6	$136.84	5.472%	$144.3279	$144.33	$144.35	$144.30
Purchase #7	$25.50	5.606%	$26.9295	$26.93	$26.95	$26.90
7 purchase totals =	$910.50		$958.5410	$958.54	$958.60	$958.50