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	$237.69	5.841%	$251.5735	$251.57	$251.55	$251.60
Purchase #2	$80.52	11.376%	$89.68	$89.68	$89.70	$89.70
Purchase #3	$75.43	11.218%	$83.8917	$83.89	$83.90	$83.90
Purchase #4	$112.60	6.192%	$119.5722	$119.57	$119.55	$119.60
Purchase #5	$171.90	9.349%	$187.9709	$187.97	$187.95	$188.00
Purchase #6	$41.68	6.851%	$44.5355	$44.54	$44.55	$44.50
Purchase #7	$196.28	10.676%	$217.2349	$217.23	$217.25	$217.20
7 purchase totals =	$916.10		$994.4587	$994.45	$994.45	$994.50