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	$154.76	3.291%	$159.8532	$159.85	$159.85	$159.90
Purchase #2	$31.98	4.719%	$33.4891	$33.49	$33.50	$33.50
Purchase #3	$179.80	3.523%	$186.1344	$186.13	$186.15	$186.10
Purchase #4	$124.31	10.176%	$136.9598	$136.96	$136.95	$137.00
Purchase #5	$141.27	9.613%	$154.8503	$154.85	$154.85	$154.90
Purchase #6	$29.58	7.807%	$31.8893	$31.89	$31.90	$31.90
Purchase #7	$113.41	4.529%	$118.5463	$118.55	$118.55	$118.50
7 purchase totals =	$775.11		$821.7224	$821.72	$821.75	$821.80